AQA AS Physics

Topic Questions

5.3 Circuits & The Potential Divider

1a2 marks

A student is given four resistors of resistance 4.0 Ω, 5.0 Ω, 2.5 Ω and 6.0 Ω respectively. 

Draw the arrangement, using all four resistors, which will give the largest resistance and calculate the resistance of this arrangement.

1b3 marks

Draw the arrangement, using all four resistors, which will give the smallest resistance and calculate the resistance of this arrangement.

1c2 marks

The four resistors are now connected to a battery of emf 12 V and negligible internal resistance, as shown in Figure 1. 

Figure 1

5-3-s-q--q1c-medium-aqa-a-level-physics

Calculate the total resistance in the circuit.

1d4 marks

The circuit is now modified to the one shown in Figure 2. 

Figure 2

5-3-s-q--q1d-medium-aqa-a-level-physics

Calculate the voltage across the 3.0 Ω resistor.

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2a3 marks

In Figure 1 below the battery, of negligible internal resistance, has an emf of 40 V. The p.d. across the lamp is 4.0 V and its resistance is 6 Ω. 

Figure 1

5-3-s-q--q2a-medium-aqa-a-level-physics

Calculate the total resistance of the circuit.

2b2 marks

Calculate the potential difference between points A and B.

2c2 marks

Show that the power of the lamp is about 3 W.

2d2 marks

What percentage of the total power supplied is dissipated in the lamp?

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3a2 marks

Figure 1 shows a potential divider consisting of a fixed resistor in series with a light dependent resistor (LDR). The voltmeter connected in parallel with the light dependent resistor has an infinite resistance. The battery has an emf of 20 V with a negligible internal resistance. 

Figure 1

5-3-s-q--q3a-medium-aqa-a-level-physics

Calculate the reading on the voltmeter when the light dependent resistor has a resistance of 1350 Ω.   

3b3 marks

The voltmeter is now connected in parallel with the fixed resistor as shown in Figure 2. 

Figure 2

5-3-s-q--q3b-medium-aqa-a-level-physics

The light intensity in the room is increased. 

State and explain what happens to the resistance of the LDR and the reading on the voltmeter.

3c4 marks

The circuit in Figure 2 is used as a simple light sensing circuit. When the voltmeter reading falls below 7.5 V, this acts as a signal which switches on a safety lamp when it is dark. 

Calculate the minimum resistance of the LDR for the safety light to come on when it is dark.

3d2 marks

The LDR has a resistance of 15.5 Ω when fully illuminated. 

Calculate the value on the voltmeter when the LDR is fully illuminated.

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4a3 marks

The circuit shown in Figure 1 can be used as an electronic thermometer. The battery has negligible internal resistance. 

Figure 1

5-3-s-q--q4a-medium-aqa-a-level-physics

The reading on the digital voltmeter can be converted to give the temperature of the thermistor T which is used as a temperature sensor. 

Explain what happens to the reading on the voltmeter as the temperature of the thermistor decreases.

4b3 marks

The graph shown in Figure 2 shows how the resistance of the thermistor varies with temperature. 

Figure 2

5-3-s-q--q4b-medium-aqa-a-level-physics

The reading on the voltmeter is 2.9 V when thermistor T has a temperature of 80°C. 

Calculate the potential difference of the battery.

4c2 marks

Calculate the current in the circuit when thermistor T has a temperature of 80°C.

4d2 marks

Calculate the power that has to be removed from the thermistor T to maintain the temperature at 80°C. 

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5a2 marks

Figure 1 below shows a bulb connected in a circuit with two resistors, an ammeter and a battery of emf 25 V and negligible internal resistance. 

Figure 1

5-3-s-q--q5a-medium-aqa-a-level-physics

The current through the ammeter is 15.0 mA. 

Calculate the p.d. across the 1850 Ω resistor.

           

5b2 marks

Calculate the resistance of the parallel combination of the resistor and the bulb.

5c3 marks

Calculate the resistance of the bulb.

5d3 marks

The bulb is replaced with another identical bulb with lower resistance. 

State and explain what happens to the p.d. across the 1850 Ω resistor.

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