Potential Difference & Power (Cambridge (CIE) A Level Physics)

The power P dissipated in a resistor of resistance R is measured for a range of values of the potential difference V across it.

The results are shown in the table in Fig. 1.1. 

Fig. 1.1.

For the table in Fig. 1.1   

i) Add the correct units.

[1]

ii) Complete the missing data.

[1]

iii) Identify errors in the recorded the data and correct them.

[1]

Complete the graph of the data on Fig. 1.2. below.    

 Fig. 1.2.

i) Plot the two missing points and complete the graph.

[3]

ii) Determine the gradient of the graph.

[3]

iii) Use the gradient of the graph to obtain a value for R.

[1]

The rest of this question is based on the data in the table Fig. 1.1 in part (a).

i) Determine the value of R when V = 3.50 V.

[1]

ii) The uncertainty in V is ± 0.01 V.

The uncertainty in P is ± 0.05 W.

Calculate the percentage uncertainty in the value of R calculated in part (i).

[3]

iii) Hence calculate the uncertainty in the value of R.

[1]

iv) State and explain whether the value of R you calculated in part (i) is consistent with the value of R you determined from the gradient in part (b).

[2]

The table in Fig. 1.1 shows the power output of three heaters. All the manufacturers claim that the heaters are rated to 1500 W. 

Fig. 1.1

Determine the most efficient heater. 

Explain how these heaters can be made more efficient. 

Calculate the work done by heater A when operating for 20 minutes. 

Two different heaters X and Y with the same internal resistance, 5R use currents of I and 2I respectively. 

State the magnitude of the power of Y in terms of I and R. 

A student is investigating the brightness of light bulbs in different arrangements connected to a 230 V power supply. One such arrangement is shown in Fig. 1.1.

Fig. 1.1

All the lightbulbs are identical. They are all rated 15 W and 230 V. The student claims the bulbs in this arrangement are all of equal brightness. 

Determine and then explain whether the student is correct. 

A different experimental arrangement is shown in Fig. 1.2. Two bulbs are connected in series with a corresponding voltmeter in parallel. 

Fig. 1.2

Calculate the current needed for both lamps to operate. 

Explain why the voltmeter must be connected in parallel with the bulb. 

In a further experimental set-up as shown in Fig. 1.3. Four identical bulbs are all connected in parallel with each other and to a power supply of 230 V.

Fig. 1.3

State and explain the value of the potential difference across each bulb assuming there is no internal resistance in the power supply, the bulbs or the wires.