Year 9 Science · Unit 3 · Lesson 17
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Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
Voltage measures the rate at which charge flows past a point in a circuit.
Correct it:
A voltmeter is connected in series with the component it measures.
Correct it:
Opening a switch anywhere in a single loop stops the current everywhere in that loop.
Correct it:
Resistance is the opposition to the flow of current.
Correct it:
In a wire, electrons flow from the positive terminal of the battery to the negative terminal.
Correct it:
1. Conventional current is drawn from the positive terminal to the negative terminal, but electrons in a wire move the other way. Explain why using conventional current does not cause problems when we analyse circuits.
Scenario: Mia’s torch
Mia builds a simple torch circuit for a school experiment. She connects a 1.5 V cell, a switch and a small lamp using copper wires. When she closes the switch, the lamp lights, but only dimly.
2. Explain what voltage, current and resistance each mean in Mia’s circuit. For each one, name the part of her circuit where it matters most.
Cause and effect: why the lamp glows
Complete the chain. Each box is caused by the one before it.
3. Suggest TWO changes Mia could make so that her lamp glows more brightly. Explain the scientific reason for each change.
Data: running a caravan on a 12 V battery
A family’s caravan has a 12 V battery that stores 1,200 Wh when it is full. A watt-hour (Wh) is the energy used by a 1 W device in one hour, so energy (Wh) = power (W) × time (h).
| Device | Current drawn (A) | Time used each day (h) |
|---|---|---|
| Fridge | 4.0 | 10 |
| Water pump | 5.0 | 0.5 |
| LED light strip | 1.5 | 5 |
| USB phone charger | 2.0 | 2 |
Source: sample values for this worksheet.
4. Complete the table. Use P = V × I for the power (every device runs at 12 V) and E = P × t for the energy each day. The fridge is done for you.
| Device | Power (W) | Energy each day (Wh) |
|---|---|---|
| Fridge | 48 | 480 |
| Water pump | ||
| LED light strip | ||
| USB phone charger |
5. (a) Calculate the total energy the devices use each day. (b) Which device has the highest power, and which uses the most energy each day? Explain why they are not the same device.
(a) Total each day Wh
6. The family wants to camp for two days without recharging the battery. Will a full battery last? Use your results to explain, and recommend changes that would make it last the two days.