Powering the Future with Energy Forms

Electrical energy and power are fundamental concepts in understanding how electricity functions and is used in our daily lives. Electrical energy refers to the energy carried by moving electric charges through a conductor, which powers devices and appliances, and is measured in joules or kilowatt-hours. Electrical power, on the other hand, is the rate at which electrical energy is consumed or produced, measured in watts, showing how quickly energy is transferred within a circuit.

Transformers play a crucial role in electrical systems by adjusting voltage levels through the principle of electromagnetic induction. They consist of primary and secondary coils wrapped around an iron core, with a changing magnetic field inducing voltage. The ratio of turns between these coils determines if the transformer increases (step-up) or decreases (step-down) voltage. This helps in energy efficiency, minimising power loss during transmission and ensuring safe voltage levels for various applications.

KEY IDEAS

• Electrical Energy: Energy carried by moving electric charges through a conductor, powering devices like lights and appliances. It is measured in joules (J) or kilowatt-hours (kWh).

• Electrical Power: Electrical power is the rate at which electrical energy is used or produced.

• Principle of the Transformer: Works on electromagnetic induction, where an AC current in the primary coil creates a magnetic field, inducing voltage in the secondary coil.

• Electrical circuit: An electrical circuit consists of various components that work together to control and direct the flow of electric current (flow of charged particles) in the way desired by the user.

• Appliance troubleshooting: Appliance troubleshooting is the systematic approach of diagnosing problems in household appliances and finding solutions to fix them.

• Energy audit: An energy audit thoroughly examines energy use in a building to identify inefficiencies and savings opportunities

Before you begin with this lesson, give the following questions a thought:

1. Have you imagined what your community would be like without light?

2. Have you experienced lights out at home before?

3. What is the source of power for electrical appliances?

Concept of Electrical Energy

Electricity is a form of energy that comes from the movement of tiny particles called electric charges. These charges move through materials known as conductors, such as metals, creating an electric current. An electric current, which is the flow of charges, is measured in units called amperes (A).

An electric current is powered by voltage, also called electric potential difference. Voltage acts like a “push” that makes electric charges flow through a circuit. A circuit is a pathway for the flow of electric current. It consists of parts like a power source, wires, switches, resistors, and capacitors.

Electricity is generated from different sources. These sources can be renewable, like water (hydro), wind, sunlight (solar), heat from the earth (geothermal), or non-renewable, like coal, oil, natural gas (fossil fuels), and nuclear materials.

Once electricity is produced, it travels through wires over long distances to reach homes, schools, and businesses.

Although electricity is very helpful, it is important to handle it safely. Without care, it can cause harm, such as electric shocks or fires. Always follow safety measures when using electricity.

Components of an Electrical Circuit

Electric circuit components work together to control and direct the flow of electric current (flow of electrons) in the way desired by the user. They are usually represented by symbols in a circuit diagram. Examples of circuit components, their functions and symbols are given in the table below:

Table 4.1: Components of an electrical circuit Basic component Function Circuit symbol Battery Provides direct current (DC) through a chemical reaction.

Power Supply Converts AC from the mains to a stable DC voltage Connecting wires Provide a path for current to flow between components Light Bulbs Convert electricity into light Switches For opening or closing a circuit, controlling the current flow.

Fuses • Provide overcurrent protection by breaking the circuit if the current exceeds a certain level.

• Protect the circuit from high voltages Resistors Control current flow and distribute voltage.

Inductors: Store energy in a magnetic field when current flows through them.

Diodes Allow current to flow in one direction only.

Basic component Function Circuit symbol Transistors Act as switches or amplifiers.

Ammeter Measures current flowing a circuit Voltmeter Measures voltage/potential differences in a circuit Transformer Change the voltage level in AC circuits.

Light emitting diodes Indicates presence of current flow in a circuit Capacitors Stores electrical charges

Activity 4.1 Identification of Components of an Electrical Circuit Copy and complete the following table using the internet and other sources for your research.

Name of circuit component Symbol Function Inductor Stores electrical energy in a magnetic field.

Transistor Transformer For stepping voltage up and down Stores electrical energy in the form of charges.

Variable resistor We have all, in one way or the other, seen or used cells and batteries in everyday life (see figure 4.1). We have often used the torchlight at home during lights off or when sent on an errand to light our way.

Figure 4.1: Cells and Batteries

Batteries: Making of electrical cells Electrical cells, commonly known as batteries, store chemical energy. This can then be converted into other energy forms, based on the energy need of the user.

The cell is a fundamental unit of the battery.

The energy stored by the cell is within the bonds of the chemical substance of the cell. This energy can power the energy needs of a wide range of electronic devices.

A simple cell consists of two terminals called electrodes, dipped in a container holding a charged liquid substance called electrolyte. In some cells, the container acts as one of the electrodes. Both electrodes are charged. The positively charged electrode is known as an anode while the negatively charged electrode is known as a cathode — see Figure 4.2.

Figure 4.2: A simple zinc-carbon cell

Activity 4.2 Making a Simple Zinc-Carbon Cell

What you need:

• Zinc strip (cathode), Carbon rod (anode)

• Manganese dioxide and carbon (graphite) mixture (cathode paste).

• Ammonium chloride solution (electrolyte).

• Paper or cloth separator and plastic or metal container.

What to do:

1. Place the zinc strip into the container at the bottom (anode).

2. Pour the ammonium chloride solution into the container to submerge the zinc strip.

3. Insert the paper or cloth separator to cover the zinc strip.

4. Apply the cathode paste (manganese dioxide and carbon powder mixture) around the

5. carbon rod.

6. Place the carbon rod with the cathode paste into the container, ensuring the separator

7. separates it from the zinc strip.

8. Seal the container to prevent leakage.

9. Attach metal strips to the zinc strip and carbon rod to create external connections.

10. Connect this battery using crocodile clips to a light-emitting diode (LED), ensuring correct polarity.

Figure 4.3: A sample of Zinc-Carbon Cell Observation The LED will emit some light. The intensity of the light depends on the voltage produced by the cell. Several cells will be required to produce a higher voltage for a brighter light.

Safety precautions

1. Wear the recommended laboratory gear to protect the skin from contact with chemical.

2. Work in a well-ventilated area to avoid inhaling fumes.

Activity 4.3 Making a Cell from a Citrus Fruit From our previous lessons on acids, bases and salts, explain why molten or aqueous solutions of acids, bases and salts are good electrolytes.

Organise yourselves into groups of no more than five for this activity.

What you need:

• Citrus fruit, e.g., lemon, lime, orange, grapefruit.

• Copper nail, screw, or wire, 5 cm long.

• Zinc nail or screw or galvanized nail about 5 cm long.

• Small holiday light with 5 cm long copper wires to connect to the nails.

What to do:

1. Set the fruit on a table and gently roll it around to soften it up, for the juice to flow inside the fruit without breaking its skin. Alternatively, squeeze the fruit with your hands.

2. Insert the zinc and copper nails into the fruit so that they are about 5 cm apart. Avoid puncturing through the end of the fruit.

3. Remove enough insulation from the copper wires so that you can wrap one around the zinc nail and the other around the copper nail. Use electrical tape or alligator clips to keep the wire from falling off the nails.

4. Connect the second nail — see Figure 4.4.

Observation When the second nail is connected, the light must come on.

Figure 4.4: A Lemon Cell

How the Lemon Battery Works

1. The copper and zinc metals act as positive (anode) and negative (cathode) battery terminals respectively.

2. The zinc metal reacts with the acidic lemon juice (citric acid) to produce zinc ions (Zn2+) and electrons (2e-). The zinc ions go into solution in the lemon juice while the electrons remain on the metal.

3. The wires of the small light bulb are electrical conductors. When they are used to connect the copper and zinc, the electrons that have built upon the zinc flow into the wire. The flow of electrons causes the flow of electric current or electricity which lights the light bulb.

4. Eventually, the electrons make it to the copper. If the electrons didn’t go any farther, they’d eventually build up so that there wouldn’t be a potential difference between the zinc and the copper. If this happened, the flow of electricity would stop. However, that won’t happen because the copper is in contact with the lemon.

5. The electrons accumulating on the copper terminal react with hydrogen ions (H+) floating free in the acidic juice to form hydrogen atoms. The hydrogen atoms bond to each other to form hydrogen gas.

In our previous activity, we built simple cells, now let us move further and build a functional electrical circuit.

Activity 4.4 Virtual Functional Electrical Circuit

What to do:

1. Carry out research using the internet and other sources and create a chart or poster on how to construct electrical circuit.

2. Think about the steps involved in constructing a functional electrical circuit.

3. Share your findings with your peers for discussion and feedback.

Activity 4.5 Constructing Functional Electrical Circuit

Note

This activity should be conducted under the supervision of a teacher.

What you need: power source (battery or power supply), conductors (wires), load (LED, motor, etc.), control devices (switches), protective devices (resistors, fuses), breadboard or PCB (for assembly), multimeter (for testing), wire strippers, soldering iron and solder (if using PCB), pliers and screwdrivers and insulating tape or heat shrink tubing.

What to do:

1. Planning and design:

a. Define the purpose by determining the goal of your circuit (e.g., lighting a LED, powering a motor).

b. b. Create a schematic diagram by drawing a circuit diagram showing all components and their connections.

c. List all necessary components needed, e.g. resistors, capacitors, power source, etc.

d. Specify the values (e.g., resistor values in Ohms) and ratings (e.g., voltage and current) for each component.

2. Preparing the components:

a. Verify that all components are working and rated for your circuit.

b. Cut wires to the necessary lengths and strip the ends for connections.

3. Build the circuit:

a. Use a breadboard by placing components on the breadboard according to your schematic diagram. Use jumper wires to connect components as per the circuit diagram. Ensure all connections match your schematic diagram.

b. Use software or a pre-made design for the PCB layout.

c. Create the PCB if you’re making it yourself or order it from a manufacturer.

d. Insert components into the PCB holes.

e. Solder each component led to the PCB pads, ensuring solid electrical connections.

f. Inspect solder joints: Check for cold solder joints or bridges that could cause shorts.

4. Testing:

a. Check for correct placement and secure connections.

b. Power the circuit with a lower voltage (if possible) to check for obvious issues.

c. A multimeter measures voltages and currents at different points in the circuit.

d. If the circuit does not work, recheck connections and component orientations. Look for short or open circuits.

5. Final assembly and safety:

a. Ensure all components are securely mounted.

b. Use insulating tape or heat shrink tubing to cover exposed wires and prevent shorts.

c. If the circuit will be used in a specific environment, consider placing it in an enclosure to protect it.

Activity 4.6 Constructing a Simple LED Circuit

What you need: 9V battery, LED (any colour), resistor (330 Ω suitable for a 9v battery and standard led), breadboard, connecting wires, multimeter (for testing), battery clip (for connecting the 9v battery to the breadboard), wire strippers and pliers (optional).

What to do:

1. Insert the Resistor:

• Place one end of the resistor in one row on the breadboard.

• Place the other end of the resistor in the next row over.

2. Connect the LED:

• Insert the longer leg (anode (+)) of the LED into the same row as one end of the resistor. (You can twist them if there is no bread board or connect them with wire)

• Insert the shorter leg (cathode (−)) of the LED into a separate row.

3. Connect the Battery:

• Take the battery clip and connect the red wire (positive) to the row with the free end of the resistor.

• Connect the black wire (negative) to the row with the LED’s shorter leg (cathode).

4. Power On: Attach the battery to the battery clip. — see Figures 4.5 to 4.6.

Figure 4.5: A simple LED circuit

Figure 4.6: A Simple LED Circuit Diagram

Observation The LED should emit light when the circuit is powered. If it does not, recheck connections and component orientations.

Safety Precautions

1. Ensure all connections are secure before powering the circuit.

2. Do not touch live wires or components with bare hands.

3. Disconnect power before adjusting the circuit.

Test yourself!

1. Why is it necessary to use a resistor in this circuit, and what might happen if it is not included?

2. How does the orientation of the LED’s anode and cathode affect the circuit’s operation? What will happen if they are connected incorrectly?

3. What does the voltage drop across the LED tell us about how energy is used in the circuit?

4. If you measured no current or the LED did not light up, what steps would you take to troubleshoot the circuit?

Explanation And Calculation of Electric Current,

Resistance and Voltage

Electric current: happens when electric charges move or flow in one direction.

In materials such as metals, which are good conductors, these charges are carried by free electrons. Metals have a structure where the outer electrons of their atoms are loosely held. These electrons break away and move freely within the metal.

This movement of electrons creates an electric current. When the metal atoms lose these electrons, they become positively charged. Copper and silver are among the best materials for conducting electric current.

An electric current is the rate at which electric charge flows. If the current stays the same over time, we can calculate it using this formula:

Q = I × t Where:

I = the current (in amperes, A), Q = the electric charge (in coulombs, C), t = the time (in seconds, s).

If the current changes over time, this formula gives the average current. On a graph of charge (y-axis) versus time (x-axis), the slope (or gradient) of the line tells you the current at a specific moment.

Voltage: a measure of how much energy a charge has at a specific point in a circuit. It’s like how high up a ball is before it falls. Voltage is always measured between two points, and one of those points is often chosen as a reference point called “ground.” Voltage is also called electromotive force (emf).

If there is a potential difference between two points, it means that the charge has different amounts of energy at each point. A voltage drop happens when the charge loses energy, while an emf means the charge gets more energy.

To find the energy transferred in a circuit, you can use this formula: E = V × Q Where:

E is the energy transferred (in joules, J), V is the voltage or potential difference (in volts, V), Q is the charge that flows through the circuit (in coulombs, C).

Resistance: Electrical resistance is a measure of the opposition to flow of current in an electrical circuit. The electrical resistance of a conductor is dependent on the following factors:

• The cross-sectional area of the conductor

• Length of the conductor

• The material of the conductor

• The temperature of the conducting material Electrical resistance is directly proportional to length (L) of the conductor and inversely proportional to the cross-sectional area (A). It is given by the following relation:

R = ρL/A Where:

R = resistance (in ohm, Ω), ρ = resistivity of the material (in ohmmeter, Ω) L = length of material (in meter, m) A = cross-sectional area of material (in squared meter m²).

Question: Write your answer in your notebook.

1. How are electric current, resistance and voltage related?

Next, you will examine Ohm’s law which brings together electric current, resistance and voltage proportionally.

Extension activity: Research on Ohm’s law using the internet and other sources.

Make notes of your findings and engage in a class discussion to share what you have learnt.

Now, let us do it together!

Ohm’s law Ohm’s Law states that, at constant temperature, the electric current flowing in a conducting material is directly proportional to the applied voltage and inversely proportional to the resistance. Mathematically, for a wide variety of substances, I ∝ V.

• At a constant temperature, resistance, R, of any given conductor remains constant.

• This implies IR = V or V = IR

• Note that for different conductors, R varies according to their characteristics (nature of material and dimensions).

• From V = IR, R= V/I, where V is in volt (V) and I in ampere (A).

• Then, the unit of R = VA–¹. This is called ohm (Ω) Now, examine the following worked examples in pairs:

Worked Examples:

1. What is the voltage if a component with a resistance of 25 Ω has a current of 250 amperes flowing through it?

Solution:

V = I × R V = (250) (25) = 6,250 volts

2. What is the current produced by a voltage of 240 V through a resistance of 0.2 Ω?

Solution:

I = V/I I = 240/0.2 = 1200 A

3. What voltage is necessary to produce a current of 200 amperes through a resistance of 100 Ω?

Solution:

V = I × R V = 200 × 100= 20000 volts (V)

4. What resistance would produce a current of 120 amps from a 6-V battery?

Solution:

R = V/I I = 6/120 = 0.05ohms (Ω)

Activity 4.7 Explanation of Ohms law What you need:

• Power Source (Battery or DC Power Supply)

• Three Different Resistors (with different resistance values)

• Multimeter (to measure current and voltage)

• One Breadboard, connecting wires, alligator clips (optional) and switch (optional) What to do:

1. Set up the circuit:

a. Connect the battery to the breadboard.

b. Insert the resistor (start with the lowest value resistor) into the breadboard.

c. Connect the multimeter in series to measure the current and in parallel to measure the voltage across the resistor.

2. Measure current and voltage:

a. Turn on the power supply and measure the current (I) flowing through the resistor and the voltage (V) across the resistor.

b. Record the values for voltage (V) and current (I).

3. Change the resistance:

a. Swap the resistor with a medium-resistance and a high-resistance resistor.

b. For each resistor, measure and record the current and voltage again.

c. Calculate Resistance for each resistor using the Ohm’s Law:

R = V/I

4. Compare your calculated resistance with the actual value printed on the resistor.

Answer the following questions in your notebook:

1. How close are the values?

2. What happens when the resistance increases?

3. What happens when the voltage increases?

4. Why is Ohm’s Law important?

Series and Parallel Connections

Most circuit components have more than one path by which they receive electricity.

These components are commonly connected in a circuit in one of two ways. These are series and parallel connections.

Series connection A series connection has the following characteristics:

1. Single path: There is only one path for the electric current to flow through the circuit.

2. Same current: The current is the same through all components in the circuit.

That is to say all circuit components share the same source current.

3. Voltage drops: The voltage drops across each component can be different, and depends on the resistance or capacitance of that component.

4. Total resistance: The total resistance of the circuit is the sum of the individual resistances.

5. Total voltage: The total voltage of the circuit is the sum of the individual voltage drops.

6. Broken circuit: If the circuit is broken at any point, no current will flow.

7. Components arranged in a line: The components are arranged in a line, with the positive end of each component connected to the negative end of the previous component.

Figure 4.7: An Electric Circuit Connected in Series

Figure 4.8: A schematic series circuit connection To save time in drawing circuits, we will need to use diagrams as shown in Figure 1.6 above. The symbols for each component can be found in the table at the beginning of this section. In any of these circuits, the precise shapes of the wires that connect the elements don’t really matter. We only need to care about the circuit components and how they are connected to other components in the circuit.

Resistors in a Series Circuit

Figure 4.9: Resistors in series Consider the resistors R₁and R₂in the schematic series circuit in Figure 4.9.

• The same current flows through both resistors. Then according to Ohm’s law, the drops in potential across the two resistors are IR1 and IR2.

• If the gain in potential across the battery is V, then the sum of these potential drops must be equal to V.

• So then, IR1 + IR2 = V ⇒ V = I (R1 + R2) = IRT where the equivalent resistance (RT) of the pair is the sum, R1 + R2.

• For an N number of resistors in series then, the equivalent resistance given by:

R_(T)= R₁+ R₂+ R₃+ …R_(N).

Current in a series circuit Consider the following resistors in series. Let I₁, I₂and I₃be the current flowing through R₁, R₂and R₃respectively.

Figure 4.10: Total current in a series circuit Then due to Kirchhoff’s first law, the same current passes through all resistors.

Thus, total current, I_(T)= I₁=I₂= I₃. To find the current in the circuit, we apply Ohm’s law. Since I = V/R, that implies I_(T)= V_(T)___ R_(T) , where V_(T)and R_(T)are total voltage and resistance respectively.

Voltage in a series circuit The voltage applied to a series circuit is equal to the sum of the individual voltage drops.” This simply means that the voltage drops must add up to the voltage coming from the battery or batteries.

Thus, for an N number of loads with a total voltage V_(T)of the circuit, V_(T)= V₁+ V₂+ V₃+ …… V_(N).

Worked Examples

1. In a series circuit with resistors of 8Ω and 12Ω, and a voltage supply of 40V, calculate the voltage drop across each resistor.

Solution:

R_(T)= 8 + 12 = 20 Ω Current (I) I = V/R = 40/20 = 2A Voltage drops across 8Ω resistor: V = I × R.

V = 2 × 8 = 16V.

Voltage drops across 12Ω resistor: V = I × R.

V = 2 ×12 = 24V.

2. A series circuit has two resistors, 10Ω and 20 power supply. Calculate the current through the circuit.

Solution:

Total resistance: R{total} = 10 + 20 = 30 Ω.

Current (I) I = V/R I = 60/30 = 2A

3. Calculate the total resistance in the circuit below.

Solution:

Total resistance, R_(T)= R₁+ R2 + R₃ R_(T)= 10 + 20 + 30 = 60Ω.

4.

What is the total resistance of the circuit above?

Solution:

Total resistance, R_(T)= (4 + 2) Ω = 6Ω.

Activity 4.8 Demonstrate Voltage in a Series Circuit

What you need: battery (e.g., 9V), three resistors (or light bulbs) with different resistance values, connecting wires, multimeter (to measure voltage), breadboard (optional) and switch (optional) What to do:

1. Build a simple Series circuit:

a. Connect the battery, resistor 1, resistor 2, and resistor 3 in series using wires.

b. The positive terminal of the battery should be connected to one end of resistor 1, and the other end of resistor 1 should be connected to the second resistor, and so on.

2. Use the multimeter to measure the total voltage across the entire circuit (across the battery). The total voltage should equal the battery voltage.

3. Measure the voltage drop across each resistor. Note the readings for each resistor.

4. Add the voltage drops across the resistors. Find that the sum of the individual voltage drops equals the total voltage supplied by the battery.

Answer the following questions in your notebooks:

1. What happens to the voltage drop if a resistor is added or removed from the series circuit?

2. How does the resistance of each component affect the voltage drop across it?

Parallel Circuit

A parallel circuit is a way of connecting electrical components in a circuit so that they form multiple paths for current flow. In a parallel circuit, all components are connected across each other (see Figure 4.11). It has the following characteristics:

1. Multiple paths: Has more than one path for current to flow through.

2. Same voltage: The voltage across each component is the same.

3. Total current: The total current flowing from the source is equal to the sum of the currents through each path.

4. Branched pathways: Devices are connected along branched pathways.

5. Resistance: The total resistance decreases as the number of branches increases.

6. Current division: Current divides among the branches of the circuit.

7. Current recombination: Current recombines on the other side of the components to the same total current.

8. Broken path: If one of the parallel paths is broken, current will continue to flow in the other paths.

9. Battery life: If batteries are connected in parallel, the battery life is multiplied by the number of batteries.

Figure 4.11: Loads (lamps) connected in parallel

Figure 4.12: Diagram of a parallel circuit Resistors in a parallel circuit For an N number of resistors connected in parallel, total resistance, 1__ R_(T) = 1/R₁ + 1/R₂ + 1/R₃ Worked Examples

1. Use the diagram below to answer the question.

Given the voltmeter shown in the above diagram can be taken to have an infinite resistance find:

a. the total resistance of the circuit.

b. the current drawn from the cell.

c. the reading on the voltmeter.

Solution

a. First, work out a series combination, then combine with 10Ω resistance.

Work in this order as the 10Ω is in parallel with both 25Ω and 40Ω.

Total resistance in series = 25 + 40 = 65Ω. This is in parallel with the 10Ω resistance.

Total resistance of the circuit, 1__ R_(T) = 1/10 + 1/65 R_(T)= 10 × 65/65 + 10 = 650/75 = 8.67Ω.

b. The total current is the voltage supply divided by the total resistance:

Current (I) I = V___ RT = 12/8.67 = 1.38A

c. The current through the final branch of the circuit is:

Current(I) I = V/R = 12/65 = 0.18A

2. Use the diagram below to answer the question.

What is the total resistance of the circuit?

Solution:

Total resistance in series = 4 + 8 = 12Ω. This is in parallel with the 12Ω resistance.

Total resistance of the circuit = 1__ R_(T) = 1/12 + 1/12 R_(T)= 12 × 12/12 + 12 = 144/24 = 6 Ω.

3. Determine the equivalent (total) resistance for each of the following circuits below.

Solution

a. 1___ R_(T) = 1/7+ 1/5+ 1/2 = 59/70 = 1.2Ω

b. RT = 2 + 5 = 7Ω

c. RT = 2 + 5 + 7 = 14Ω.

Activity 4.9 Parallel Arrangement of Resistors in Electrical Circuit What you need: breadboard, resistors, wires, multimeter What to do:

1. Connect resistors in parallel on a breadboard.

2. Measure the voltage across each resistor to confirm they are the same.

3. Measure the total current by placing the ammeter in series with the power source and the current through each resistor by placing the ammeter in series with each resistor in turn.

4. Calculate the equivalent resistance and compare it with the measured values.

Power Power is the rate at which work is done, or energy is transferred over time. It is a measure of how quickly energy is used or produced. The standard unit of power is the watt (W). This is equivalent to one joule per second (J/s).

• The formula for power is: Power = Workdone________ Time taken

• In terms of energy, Power = Energy transfered_____________ Time taken

• In symbols, P = W/t Where:

P is power (in watts, W), W is work done, or energy transferred (in joules, J) t is time (in seconds, s).

Worked Example

If the power rating of an incandescent light bulb is 60 watts (W) and the bulb is used for 5 hours a day, what is its total energy used per day?

Solution

60 W × 5 hours = 300 Watt-hours (Wh) or 60 W × (5 × 60 × 60) s = 1,080,000 Joules (J) Electrical Power In electrical circuits, power is the rate at which electrical energy is consumed or produced by a component, such as a resistor, motor, or generator.

The formula for electrical power is: P = V × I Where: P = power (in watts, W), V = voltage (in volts, V) and I = current (in amperes, A).

For resistive loads, the power can also be expressed by combining the formula above with Ohm’s Law (V = I × R). Thus, P = I²× R. Also, P = V²__ R Worked Examples

1. A kettle rated at 2000 W boils water in 5 minutes. Calculate the energy used by the kettle.

Solution

Energy = Elecrical power × time Energy = 2000W × 300s = 600000J The kettle converts 600,000 joules of electrical energy into heat energy.

2. A phone charger operates at 5 V and draws 2 A of current. Calculate the power consumed by the phone charger.

Solution

P = VI = 5 × 2 = 10W.

The charger consumes 10 watts of power to charge the phone.

3. An electric heater consumes 1500W of power and operates on a voltage of 240V. Calculate the current through the heater.

Solution

P = IV Current (I): I = P ÷ V Substitute the values:

I = 1500W ÷ 240 = 6.25A.

Therefore, current through the heater is 6.25 amperes.

Appliance Troubleshooting

Appliance troubleshooting is the systematic approach of diagnosing problems in household appliances and finding solutions to fix them. This can involve inspecting the appliance for obvious issues, performing tests, and following steps to identify and resolve the malfunction. Troubleshooting household appliances can help identify and resolve common issues without professional assistance.

Components of appliance troubleshooting

1. Observation: Look for visible signs of damage, wear and tear, or anything unusual (e.g., frayed wires, broken parts, leaks).

2. Power check: Ensure the appliance receives power by checking the power cord, plug, and outlet. Test the outlet with another device to confirm it’s working.

3. Reset and restart: Some appliances have a reset button. Turning the appliance off and on or using the reset function can sometimes resolve minor issues.

4. Consult the manual: The appliance’s user manual often contains troubleshooting tips and solutions for common problems specific to the model.

5. Basic tests: Perform basic tests to check the functionality of the appliance’s components. This can include testing switches, fuses, and other easily accessible parts.

6. Sound and smell: Pay attention to unusual sounds or smells which can indicate specific issues (e.g., a burning smell could indicate an electrical problem).

7. Error codes: Modern appliances often display error codes when something goes wrong. Refer to the manual to understand the error code and follow the recommended steps to address it.

Activity 4.10 Role Play Client and Electrical Engineer

What to do:

1. Conduct this activity with a peer or a family member, where one partner acts as a ‘client’ and the other acts as an ‘electrical engineer’.

2. The client will present an issue they are facing with a common household appliance. The engineer must describe what the trouble shooting process might look like for that.

3. Use the table below as a template to conduct this activity. The first one has been completed for you:

Table 4.2: Steps in troubleshooting common appliances Common issues of household appliances Troubleshooting steps Refrigerator Not cooling:

1. Check temperature settings.

2. Clean condenser coils.

3. Ensure door seals are intact.

4. Verify vents inside the fridge are not blocked.

5. Check the drain pan and water supply line for leaks.

Leaking water:

1. Check the drain pan for overflow.

2. Inspect the water supply line for leaks. 3. Clear any clogs in the defrost drain.

Unusual noises:

1. Ensure the refrigerator is level.

2. Check for loose components inside the fridge or freezer.

Washing machine Dishwasher Oven/stove Microwave Safety precautions of household appliances

An energy audit is a careful check of how energy is used in a building to find ways to save energy and reduce waste. It involves looking at energy use, inspecting systems, and analysing how energy flows. The goal is to use less energy without reducing the things we need the energy for, like lighting, heating, or cooling. An energy audit is an important step in creating a plan to manage and save energy better.

Sources of Electrical Energy

Electricity can be made in many ways, using different sources of energy. These sources can be divided into two groups:

1. Non-renewable energy sources

2. Renewable energy sources.

Non-Renewable energy sources Non-renewable energy sources are types of energy that come from natural resources that take millions of years to form. These resources, like coal, oil, and natural gas, are used up faster than they can be replaced. Once they are gone, we cannot get more of them for a very long time.

1. Coal: Coal is burnt to make heat. The heat boils water to create steam, which spins turbines to make electricity.

2. Natural Gas: Natural gas is burnt to make heat, which produces steam or directly spins turbines to generate electricity.

3. Oil: Oil is burnt in power plants to heat water and create steam, which spins turbines to generate electricity.

Renewable energy sources Renewable energy sources are types of energy that come from natural resources that can be replaced and will not run out. These resources, like sunlight, wind, water, and plants and animal body parts. They are always available and can be used over and over again. They are also cleaner and better for the environment than non-renewable energy sources.

1. Nuclear Power: Special materials like uranium are split into smaller parts, a process called nuclear fission. This releases heat, which creates steam to spin turbines and produce electricity.

2. Hydropower: Flowing water, like from a river or dam, spins turbines connected to generators to make electricity — see Figure 4.14

3. Wind Power: Wind turbines use the power of moving air to turn their blades, which generates electricity.

4. Solar Power (Photovoltaic): Solar panels use sunlight to directly produce electricity using special materials called semiconductors — see Figure 4.13.

5. Concentrated Solar Power (CSP): Mirrors focus sunlight onto a fluid, heating it to create steam. The steam then spins turbines to make electricity.

6. Geothermal Energy: Heat from deep inside the Earth is used to create steam, which spins turbines to generate electricity.

7. Biomass: Organic materials like wood or crop waste are burnt or turned into fuels to produce steam that drives turbines and generates electricity.

8. Tidal and Wave Energy: The energy from ocean tides and waves is used to spin turbines and make electricity.

9. Hydrogen Fuel Cells: Hydrogen gas reacts with oxygen to produce electricity and water.

Figure 4.13: Solar Energy Figure 4.14: Hydroelectric Power

Energy Losses: Heating Effects of Electric Current

When electricity flows through a wire, the wire gets warm or even hot. This is called the heating effect of electric current, or joule heating. It happens because the tiny particles carrying electricity (called electrons) bump into other particles inside the wire. These bumps make the particles in the wire move faster, which causes the wire to heat up.

How does it work?

• Electric current flows through a conductor (like a wire).

• The electrons (tiny moving charges) collide with the atoms of the wire.

• These collisions make the wire’s atoms vibrate more, producing heat.

• As a result, the conductor’s temperature increases.

Examples of heating effects in everyday life

a. Electric heaters: Used in stoves, irons, and room heaters. The current heats up a wire or coil inside, which warms the air or surface around it.

b. Light Bulbs: In old-style incandescent bulbs, the electric current heats up a thin wire (filament) until it glows, producing light and heat.

c. Fuses: Fuses are safety devices in electrical systems. They contain a thin wire that melts when the current is too high, breaking the circuit to prevent damage.

Figure 4.15: Appliances using heating effect of current Problems caused by heating in electric circuits

1. Energy Loss: When wires heat up, some electrical energy is turned into heat energy. This means less energy is available to power devices. This can be a big issue with long wires, like the ones carrying electricity to your home.

2. Damage to components: Too much heat can damage wires and electrical parts, causing devices to stop working or even start on fire.

To prevent this, devices often use cooling systems like fans or metal pieces (called heat sinks) to carry away the heat.

Activity 4.11 Heating Effect of Electric Current

What you need:

• A battery or electric cell, small light bulb, a switch, connecting wires

• thermometer (optional, to measure temperature changes)

• Heat-resistant gloves (to protect your hands)

• A heat-resistant surface (like a tile or piece of glass) What to do:

1. Set up the circuit

a. Connect the battery, light bulb, switch, and wires to create a simple circuit.

b. Make sure the switch is part of the circuit so you can turn the current on and off.

c. Place the setup on a heat-resistant surface to keep things safe.

2. Check the bulb before turning it on

a. Keep the switch off.

b. The bulb will not glow, and it will feel cool or at room temperature when you touch it.

3. Turn on the circuit.

a. Flip the switch to on so that current flows through the bulb.

b. Watch the bulb light up. This shows that electrical energy is being converted into light and heat.

4. Feel the bulb after it glows

a. Let the bulb glow for one-two minutes, then turn the switch off.

b. Carefully touch the bulb using heat-resistant gloves.

c. You will notice that the bulb is warmer than it was before.

Safety Precautions

a. Always use heat-resistant gloves when touching the bulb after it has been on.

b. Make sure the wires are connected properly to avoid sparks or short circuits.

c. Be careful with the battery and wires to prevent electric shocks.

d. Perform the experiment on a heat-resistant surface to prevent any damage.

Reflect on the following questions, record your observations and answers in your notebook.

1. If the bulb did not glow or heat up, what could be wrong with the circuit?

2. How does the heating effect of electric current relate to energy efficiency in electrical devices?

3. What could happen if we left the bulb glowing for a long time without turning it off?

4. Why does the bulb’s temperature increase when the switch is turned on?

5. What would happen if we used a larger bulb or a higher voltage battery?

Electrical Energy in The Home

Calculate the energy consumed by meter reading: Electrical energy is the energy we use when we turn on lights, use TVs, or charge our phones. At home, we measure this energy using a device called an electric meter. It shows how much energy we use in a unit called kilowatt-hour (kWh).

What is a kWh?

One kilowatt-hour means you used 1,000 watts of power for one hour. For example:

A 1,000-watt heater running for 1 hour = 1 kWh.

A 100-watt light bulb running for 10 hours = 1 kWh.

How to Calculate Energy Used

Look at the numbers on your meter before and after you use electricity.

Subtract the earlier number from the later number to find out how much energy you used.

For example:

Meter reading at start: 50 kWh.

Meter reading at end: 70 kWh.

Energy used: 70 - 50 = 20 kWh.

Your electricity bill is calculated based on how many kWh you used.

Saving energy, like turning off lights when not needed, can lower your bill and help the environment.

Hint 1 kWh = 3,600,000 Joules of energy. That is enough to light up a 100-watt bulb for 10 hours

Activity 4.12 Measuring Energy Consumption of Home Appliances

What you need: Fan and lamp or a hairdryer What to do:

1. Choose a few small household appliances such as a fan, a lamp, or a hairdryer. Use a plug in power meter (or use the same energy consumption formula) to measure how much energy each appliance consumes over a specific period.

2. Record the power rating (in watts) for each appliance (fan might be 40 W, a hair dryer might be 1200 W)

3. Turn on each appliance for a set amount of time (for example 30 minutes) and calculate how much energy each appliance uses during that time.

4. Share your experience and findings with your peers or family members.

Worked Examples

1. A television rated at 150 watts is used for 5 hours a day. Calculate the energy consumed in kilowatt-hours (kWh) for a week.

Solution

Power of appliance (P): 150 W = 0.15 kW Time of usage per day (t): 5 hours Energy per day (E): E = P × t = 0.15 kW × 5 hours = 0.75 kWh Energy for a week: 7 = 0.75 kWh × 7 = 5.25 kWh Therefore, the television consumes 5.25 kWh of energy in a week.

2. A washing machine has a power rating of 2 kW and is used for 2 hours per load. If the electricity cost is Ghc 0.12 per kWh, find the cost of running the washing machine for 5 loads.

Solution

Power of appliance (P): 2 kW Time per load (t): 2 hours Energy per load (E): E = P × t = 2 kW × 2 hours = 4 kWh Total energy for 5 loads: E = 4 kWh × 5 = 20 kWh Cost of electricity = Total energy × Rate per kWh = 20 kWh × 0.12 = Ghc 2.40 Hence, the cost of running the washing machine for 5 loads is Ghc 2.40.

3. A refrigerator operates 24 hours a day with a power rating of 200 W. Calculate the total energy used in one year (365 days).

Solution

Power of appliance (P): 200 W = 0.2 kW Time per day (t): 24 hours Energy per day (E): = P × t = 0.2 kW × 24 hours = 4.8 kWh Energy per year = Energy per day × 365 = 4.8 kWh × 365 = 1,752 kWh So, the refrigerator uses 1,752 kWh of energy in a year.

Types of Meters

Analog Meter Digital Meter Smart Meter

Figure 4.16: Different types of meters How to Read Your Meter Analog meter reading

1. Identify the dials: Analog meters typically have five dials, each numbered from 0 to

2. Read each Dial: Start from the left and read each dial in sequence. Note that some dials rotate clockwise while others rotate counterclockwise.

3. Record the numbers: Write down the number that each pointer is closest to.

If the pointer is between two numbers, record the lower number.

4. Calculate usage: Subtract the previous reading from the current reading to determine the kWh used.

5. For example, if the previous reading was 12345 kWh and the current reading is 12400 kWh, you have used 55 kWh.

Digital meter reading

1. Locate the display: Digital meters have a screen that displays the total kWh used.

2. Record the number: Simply write down the number displayed. There are no dials or complex readings to interpret, making digital meters user-friendly.

Smart meter reading Smart meters can vary by brand, but the process is generally similar.

Check the display: Smart meters will have a digital display showing the total kWh.

Energy Audit Process

An energy audit helps us find out how much energy a building uses and where we might be wasting energy. It’s like checking how well our home, school, or building uses electricity, so we can find ways to save energy and money.

1. Getting started (Initial Assessment):

a. First, gather information about the building. How big is it? How old is it? What is it used for?

b. Look at electricity and energy bills from the past year. These bills show how much energy was used and if there are any changes during different seasons, like using heaters in winter or fans in summer.

2. Checking the building (Walkthrough Inspection):

a. Walk around the building to see how energy is being used.

b. Check lights, heaters, air conditioners, refrigerators, windows, and doors.

c. Look for problems like lights being left on, gaps in doors or windows where air leaks out, or old appliances that use too much energy.

3. Detailed testing (Detailed Analysis):

a. Use special tools to measure how much energy different devices or systems use.

b. Find out which appliances, like heaters or air conditioners, use the most energy.

c. Check for places where heat escapes (like gaps in the walls or windows) or where there’s poor insulation.

4. How people use energy (Evaluate occupant behaviour):

a. Observe how people use energy in the building.

b. Talk to them or ask questions to find out if they forget to turn off lights, leave appliances running, or use heaters and coolers too much.

c. Consider habits during different times of the year or work shifts.

5. Sharing the Results (Report Findings):

a. Write a report about what was found during the audit.

b. Show where energy is being wasted and suggest simple ways to fix it, like switching to energy-efficient bulbs or sealing gaps in doors and windows.

c. Prioritize the changes that save the most energy and are easy to do.

Activity 4.13 Energy Audit Investigation

Review this scenario:

The school administration wants to reduce energy consumption and costs.

They have formed an energy Audit team consisting of students, teachers, and facilities staff.

As members of the energy Audit team, conduct an energy audit of the school and energy saving measures.

What to do:

1. Look at a section of the school (e.g. classroom, library, cafeteria).

2. Take a walk-through inspection observing energy usage and identifying areas for improvement.

3. Record your findings on the worksheet named Energy Audit worksheet with the heading; Area, Energy usage and Recommendations.

Reflect on the following questions:

1. What are the most energy-intensive areas in the school?

2. How can they reduce energy consumption?

3. What are the cost and benefits of energy-efficient solutions?

Home Energy Savings Plan

Saving energy at home means using less electricity or fuel while still staying comfortable. A home energy savings plan helps you figure out where you can save energy, what to change, and how to track your progress.

Set clear goals Start by deciding what you want to achieve. Your goals should be:

1. Specific: Know exactly what you want to do.

2. Measurable: You can check your progress.

3. Achievable: Make sure your goals are possible.

4. Relevant: Focus on energy-saving tasks.

5. Time-bound: Set a deadline.

Activity 4.14 Identify Energy-Saving Opportunities

Based on an initial assessment of your home, identify areas where energy savings can be achieved. Common areas include:

Table 4.3: Energy saving plan Area What to do Why it helps Lighting 1. Replace Bulbs: Use energy- saving LED or CFL bulbs instead of old ones.

Saves electricity and lasts longer.

2. Use sensors: Install motion sensors or timers to control lights.

Lights turn off when not needed, saving energy.

3. Maximize natural Light:

Open windows and clean them to let in more sunlight.

Reduces the need for artificial lighting.

Heating, Ventilation,

and Air Conditioning (HVAC)

1. Regular Maintenance:

Check and clean your heating and cooling systems regularly.

Keeps them running smoothly and uses less energy.

2. Programmable Thermostats:

Use smart thermostats to set temperatures for different times.

Saves energy by heating or cooling only when needed.

3. Improve Insulation: Add

insulation to walls, attics, or basements.

Keeps your home warm in winter and cool in summer, using less energy.

4. Seal Leaks: Close gaps around windows and doors to stop air from escaping.

Prevents energy loss and keeps rooms comfortable.

Area What to do Why it helps Appliances and Electronics

1. Upgrade Appliances: Get

modern appliances with energy-saving ratings.

Uses less electricity than older models.

2. Use Power Strips: Plug

many devices into a single power strip to easily switch them off.

Stops devices from wasting electricity when not in use.

3. Unplug Devices: Unplug

gadgets like chargers and TVs when not in use.

Prevents “phantom power” (electricity used even when off).

Water Heating 1. Insulate Water Heater: Wrap

your water heater and pipes in insulation.

Keeps water hotter for longer and reduces energy use.

2. Install Low-Flow Fixtures:

Use water-saving faucets and showerheads.

Uses less hot water, saving energy and water.

3. Lower Temperature

Settings: Keep your water heater at 120°F (safe and efficient).

Saves energy while keeping water hot enough.

Building Envelope

1. Improve Insulation: Add

insulation to walls, attics, or basements.

Helps maintain indoor temperatures, saving energy.

2. Energy-Efficient Windows:

Replace old windows with double or triple-pane ones.

Prevents heat from escaping or entering, saving energy.

3. Seal Openings: Fix cracks and gaps around windows and doors.

Stops air drafts and reduces energy loss.

Example of home energy saving plan Goal: Reduce energy consumption by 20% within one year.

Table 4.4: Example of energy saving plan in the home.

Timeframe What to Do Why It Helps

Short- Term (0-3

Months)

1. Use LED Bulbs: Change all old bulbs to energy-saving LED ones.

Uses less electricity and lasts longer.

2. Install Smart Thermostats: Set

the temperature automatically for mornings, nights, etc.

Saves energy by heating or cooling only when needed

3. Teach Energy-Saving Habits:

Share tips with your family, like turning off lights when leaving a room.

Helps everyone work together to save energy.

4. Unplug Devices: Unplug

chargers and devices when not in use.

Stops electricity from being wasted by devices in standby mode Medium- Term (3-6 Months)

1. Upgrade Appliances: Replace

old fridges, TVs, and washing machines with energy- efficient ones.

Uses less energy for the same tasks.

2. Seal Windows and Doors:

Close gaps or cracks where air escapes.

Keeps rooms warm in winter and cool in summer without extra energy.

3. Install Low-Flow Fixtures:

Use water-saving showerheads and faucets.

Saves water and the energy used to heat it.

4. Insulate Water Heater: Wrap

your water heater and pipes to keep heat in.

Keeps water warm for longer, reducing energy use.

Long- Term (6-12

Months)

1. Add Insulation: Improve

insulation in walls, attics, and basements.

Maintains comfortable temperatures using less energy.

Timeframe What to Do Why It Helps

2. Replace Windows: Use

energy-efficient windows that stop heat from escaping.

Saves energy during both hot and cold seasons.

3. Install Solar Panels: Use

sunlight to create your own electricity.

Reduces dependence on non-renewable energy sources.

4. Apply for Incentives: Look

for government rebates or programs to save money on upgrades.

Makes it easier to afford energy-saving improvements.

Electromagnetic induction: The method through which a changing magnetic field generates a voltage in a conductor.

Primary winding: The coil that is connected to the power source input.

Secondary winding: The coil is connected to the output circuit where the modified voltage is required.

Core: The magnetic component that improves the efficiency of the magnetic flux connection between the primary and secondary coils.

Transformer A transformer is an electrical device that changes the voltage of an alternating current (AC). It can either increase (step-up) or decrease (step-down) the voltage to make it suitable for different uses.

A transformer is like a special kind of electric machine that helps change the power level to make it just right for different uses. For example, it can make power stronger to send it far away or make it safer for use at home. — See Figure 4.17

Figure 4.17: A transformer

Activity 4.15 Electromagnetic Induction in a Transformer

What you need: wire coil, magnet and small light bulb.

What to do:

1. Connect the small light bulb to the wire coil.

2. Move the magnet quickly in and out of the coil. — See Figure 4.18 Observation: The light bulb flickers.

Conclusion: The movement creates a small amount of electric power that can make the light bulb flicker. This demonstrates the principle of electromagnetic induction. This is like what happens in a transformer. Moving electricity in the primary coil makes a magnetic field, which then makes electricity in the secondary coil.

Figure 4.18: Producing Current by Electromagnetic Induction

Activity 4.16 How a transformer works What you need: battery-operated electromagnet or coil of wire and iron rod, small light bulb or LED and connecting wires What to do:

1. Wrap a coil of wire around a metal core (like a nail or bolt).

2. Connect the ends of the wire to a battery to create an electromagnet field.

3. Bring the coil close to another coil connected to a light bulb.

4. Quickly connect and disconnect the battery to show how the changing magnetic field induces a current in the second coil.

Observation: The bulb will glow shortly.

Conclusion: This shows that a changing current in the primary coil induces current in the secondary coil, like how a transformer works.

How transformer works Think of a transformer as a box with two coils of wire:

• Primary Coil: This is the coil that gets power from a power source like a power plant.

• Secondary Coil: This is the coil that sends the power out, but at a different strength.

Both coils are wrapped around a middle piece called a core, which is usually made of iron. The core helps pass the “energy message” between the coils.

The primary coil receives an electric current from a power source. This current moves back and forth quickly (alternating current, or AC).

When the current moves through the primary coil, it creates a magnetic field in the iron core. The magnetic field spreads to the secondary coil and causes an electric current to appear there too. This current has the same type of power, but it might be stronger or weaker, depending on how the coils are arranged.

Types of Transformers

Step-down transformer Imagine you have a big water pipe (the primary winding) that carries a lot of water (voltage), and a smaller pipe (the secondary winding) that carries less water. A step-down transformer works by taking the large amount of water ~(voltage) from the big pipe and squeezing it through the smaller pipe, but the smaller pipe carries the water more slowly, or at a higher flow (current).

In a transformer, there are wires instead of pipes, but the idea is similar. The primary winding (the big pipe) has lots of coils (or turns of wire), and the secondary winding (the small pipe) has fewer coils. This reduces the voltage (like reducing the pressure in the water pipe) but increases the current (the amount of water flowing through the small pipe).

In simple terms, a step-down transformer takes high voltage from the primary side, reduces it, and sends it out with more current on the secondary side. This is useful for powering things like home appliances safely. The step-down transformer has a larger number of turns in the primary winding and a smaller number of turns in the secondary winding.

Figure 4.19: Step-down Transformer

Step-up transformer A step-up transformer works the opposite way of the step-down transformer. It takes low voltage (like a small water flow) from the primary side and increases the voltage (raises the water pressure). It does this by using more coils (turns of wire) on the secondary side than on the primary side. This means that when the voltage increases, the current (or flow of electricity) decreases.

Imagine that when you increase the pressure of water in a pipe, the amount of water flowing through the pipe becomes less, but the water can travel farther.

The reason we use step-up transformers is to send electricity over long distances more efficiently. When the voltage is increased, the current is reduced, which prevents the wires from heating up too much. This makes the energy transfer safer and more efficient, especially when the electricity must travel from power stations to homes or businesses.

A step-up transformer takes a low voltage, increases it to a higher voltage, and reduces the current to make the transfer of electricity over long distances safer and more efficient.

The step-up transformer has a smaller number of turns in the primary winding and a larger number of turns in the secondary winding.

Figure 4.20: Step-up Transformer

Activity 4.17 Simulating a Step-Down Transformer

What you need:

• Two coils of wire (one with more turns and one with fewer turns)

• One small light bulb (representing a load or device that uses electricity)

• One battery (to represent the power source)

• Electrical tape, connecting wires

• A ruler or measuring tape (to measure the number of turns in each coil) What to do:

1. Take two coils of wire. Coil the first one with more turns of wire (about 20-30 turns) and the second coil with fewer turns of wire (about 10 turns).

2. Set Up the First Circuit (Simulate Step-Down Transformer):

a. Connect the first coil (with more turns) to the battery using the connecting wires. Attach the light bulb in series with the coil.

b. Turn on the circuit and observe the brightness of the light bulb. It should be bright because the voltage is higher, and the current is lower.

c. Now, swap the first coil (with more turns) with the second coil (with fewer turns). Connect the second coil (with fewer turns) to the battery and light bulb in the same way.

d. Turn on the circuit and observe the light bulb again.

Reflect on the following questions and answer them in your notebook.

1. Why did the light bulb get dimmer?

2. What would happen if both coils had the same number of turns?

3. Explain how step-down transformers are used in everyday life, such as in power supplies for home appliances.

Record your observations in terms of changes in the brightness of the bulb in your notebook.

Safety Precaution

Use proper connections in your circuit set up.

Activity 4.18 Building a Step-Down Transformer

What you need:

• Iron core (you can take this from an old transformer or buy one)

• Insulated copper wire (this is the wire we will wrap around the core, use different thicknesses for the primary and secondary coils)

• Wire cutters/strippers (to cut and strip the wire)

• Soldering iron and solder (to connect the wires safely)

• Electrical tape (to insulate the connections)

• AC signal generator (to provide the alternating current to the primary coil)

• Multimeter (to measure the voltage) What to do:

1. Calculate the Turns Ratio

a. You need to calculate how many turns of wire you will have on each coil.

For a 1:2 step-down transformer, the primary coil will have twice as many turns as the secondary coil. For example, if the secondary coil has 10 turns, the primary coil should have 20 turns.

2. Prepare the Core

a. Place the iron core on a flat surface. This core will help the electricity move through the wire and change the voltage.

b. Make sure the core is clean, with no dust or debris, to ensure it works properly.

3. Wind the Coils

a. Primary Coil: Take the insulated copper wire and wrap it around one side of the iron core. The number of turns should match the calculation you made. For example, if you’re using a 1:2 step-down ratio and the secondary coil has 10 turns, the primary coil will have 20 turns. Leave some extra wire at the ends for connecting it to the power source.

b. Secondary Coil: Next, wrap the secondary coil on the opposite side of the core. The number of turns should be half of the primary coil.

For example, if you have 20 turns in the primary coil, you will wind 10 turns in the secondary coil.

4. Connect the leads

a. Carefully connect the ends of the primary coil to the AC signal generator. This is the source of electricity that will go through the primary coil.

b. Connect the ends of the secondary coil to the multimeter (to measure the voltage output).

c. Use a soldering iron to make the connections. Be careful and use electrical tape to insulate the wires so they don’t touch each other or cause any short circuits.

5. Test the Transformer

a. Once the coils are connected, turn on the AC signal generator to send a low voltage (2V AC) into the primary coil.

b. Measure the output voltage across the secondary coil using the multimeter. The output voltage should be lower than the input voltage, according to the number of turns in the coils. For example, if you used a 1:2 ratio (primary coil = 20 turns, secondary coil = 10 turns), the output voltage should be about half of the input voltage.

If the primary coil has 2V, the secondary should have approximately 1V Reflect on the following questions and write your answers in a notebook:

1. What did you observe? If your experiment was correct, the voltage measured on the secondary coil should be lower than the voltage on the primary coil.

2. What do you think would happen if there was a problem with the primary coil of a transformer?

3. How would it affect the secondary coil and the voltage output?

Safety Precautions

1. Do not exceed a 1:10 ratio of turns in the primary and secondary coils.

This is important to keep the experiment safe.

2. Do not exceed an input voltage of 2V AC. The power supply must be locked to ensure this. This low voltage is safe for the experiment.

1. Introduction to electrical safety:

https://www.hse.gov.uk/electricity/precautions.htm

2. Power rating for common appliances:

https://www.altestore.com/pages/power-ratings-for-common- appliances?srsltid=AfmBOoo72Jhrok8vp_CC1HPu_ ho8annLWSPLsl_B_n9H3s72JgFdxCco

1. What are the functions of step-up and step-down transformers?

2. How do step-up and down transformers work?

3. How could we design a transformer to make sure it works as efficiently as possible? What materials or methods might make it better.

4. Give the units for voltage, current, power and charge.

5. A resistor has a resistance of 10 Ohms, and the current flowing through it is 2 Amps. What is the voltage across the resistor?

6. Describe the steps involved in troubleshooting household appliances.