Figure 2 shows a circuit that a student built. The lamp has a resistance of 10 Ω Each resistor has a resistance of 10 Ω What is the total resistance of the circuit? Tick (✓) one box. Between 20 Ω Exactly 20 Ω Exactly 30 Ω Less than 20 Ω Explain your answer to Question 04.1 The student replaced one of the resistors with a thermistor. Draw the circuit symbol for a thermistor in the box below. The student increased the temperature of the thermistor. Explain how the current in the thermistor changed. Figure 3 shows another circuit the student built. Explain how the potential difference across the resistor and the lamp will change when the switch is closed. The resistor The lamp

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Figure 2 shows a circuit that a student built - AQA - GCSE Physics Combined Science - Question 4 - 2019 - Paper 1

Question 4

Figure 2 shows a circuit that a student built. The lamp has a resistance of 10 Ω Each resistor has a resistance of 10 Ω What is the total resistance of the circuit?... show full transcript

Worked Solution & Example Answer:Figure 2 shows a circuit that a student built - AQA - GCSE Physics Combined Science - Question 4 - 2019 - Paper 1

Step 1

What is the total resistance of the circuit?

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Answer

The total resistance of the circuit is less than 20 Ω because the resistors are in parallel. When resistors are connected in parallel, the total resistance can be found using the formula:

$\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2}$ In this case, with two resistors of 10 Ω each, we have:

$\frac{1}{R_{total}} = \frac{1}{10} + \frac{1}{10} = \frac{2}{10} \Rightarrow R_{total} = 5 \Omega$ This value confirms that the total resistance is indeed less than 20 Ω.

Step 2

Explain your answer to Question 04.1

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Answer

The resistance of the lamp (10 Ω) is added to the total resistance of the resistors in parallel. Each of the resistors, having the same value, contributes to a total resistance that is less than the lowest individual resistor's resistance. Thus, the overall resistance remains below 20 Ω.

Step 3

Draw the circuit symbol for a thermistor in the box below.

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Answer

The circuit symbol for a thermistor is represented by a rectangle with two wires emanating from it, often depicted as follows:

    +-----+
    |     |
    |     |
    +-----+

This symbol indicates that the component is a thermistor.

Step 4

Explain how the current in the thermistor changed.

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As the temperature of the thermistor increases, the current through it also increases. This occurs because the resistance of the thermistor decreases with temperature, allowing more electrons to flow through. Therefore, using Ohm's law, an increase in current can be observed as:

$I = \frac{V}{R}$ Since R decreases, I increases.

Step 5

Explain how the potential difference across the resistor will change when the switch is closed.

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Answer

When the switch is closed, the potential difference across the resistor becomes 0 V if there is a short circuit across it. This happens because the closed switch provides a path with lower resistance than the resistor, effectively diverting current away from it.

Step 6

Explain how the potential difference across the lamp will change when the switch is closed.

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Answer

When the switch is closed, the potential difference across the lamp will be the same as the battery voltage. This is due to the fact that the circuit is now complete, allowing current to flow through the lamp, resulting in the maximum potential difference being applied to it.

Figure 2 shows a circuit that a student built - AQA - GCSE Physics Combined Science - Question 4 - 2019 - Paper 1

Worked Solution & Example Answer:Figure 2 shows a circuit that a student built - AQA - GCSE Physics Combined Science - Question 4 - 2019 - Paper 1

What is the total resistance of the circuit?

Explain your answer to Question 04.1

Draw the circuit symbol for a thermistor in the box below.

Explain how the current in the thermistor changed.

Explain how the potential difference across the resistor will change when the switch is closed.

Explain how the potential difference across the lamp will change when the switch is closed.

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