Potential Difference & Power — Structured Questions (Cambridge International A-Level Physics): Exam Questions

State the symbol and the SI unit for potential difference.

Electric charge and potential difference are related.

(i) State an equation that relates electric charge and potential difference

(ii) Write one joule in terms of units of potential difference and electric charge

A lamp is powered by a 3.0 V cell.

Calculate the work done on the lamp by a single electron in this circuit.

Extract:

A lamp is powered by a 3.0 V cell. Calculate the work done on the lamp by a single electron in this circuit. Work done by an electron with one cell, W = 4.8 × 10^−19 J

Three more identical 3.0 V cells are added in series to the circuit.

Calculate the new work done per electron.

State the correct arrangement for the equation linking power, current and resistance.

Extract:

The correct arrangement for the equation linking power, current and resistance is: P = I²R

A current of 3.6 A passes through a 20 Ω resistor.

Calculate the power transferred to the resistor. Give your answer to 2 significant figures.

Complete the sentences.

Choose answers from the box.

Each answer can be used once, more than once or not at all.

When the .............................. is increased, more energy is transferred to each coulomb of charge passing through the cell.

For a given potential difference, if .............................. is increased, then the power transferred to a component is increased.

A high current means that more power is wasted to the .............................. store of the surroundings.

Draw a voltmeter, connected correctly, to the circuit diagram in Fig 1.1 to measure the combined potential difference across the bulb and the variable resistor.

Fig 1.1

The table shows a range of household appliances, supplied with 230 V, and their power ratings.

Complete the table by adding the values for the current required for each appliance.

Extract:

The table shows a range of household appliances, supplied with 230 V, and their power ratings. Toaster power rating: 480 W.

Calculate the electrical work done by using the toaster on full power for 3 minutes.

Extract:

The table shows a range of household appliances, supplied with 230 V, and their power ratings. The Toaster has a power rating of 480 W. Calculate the electrical work done by using the toaster on full power for 3 minutes: Toaster power, P = 480 W; Time, t = 3 minutes = 180 s; W = P t = 480 × 180 = 86 400 J

Calculate the amount of charge that flowed through the toaster circuit during the 3 minutes of use. Give your answer to 2 significant figures.

Extract:

The table shows a range of household appliances, supplied with 230 V, and their power ratings. Toaster power rating = 480 W

Calculate the resistance of the toaster.

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.

ii) Complete the missing data.

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

Extract:

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. V / V | V^2 / V^2 | P / W 1.00 | 1.0 | 0.21 1.71 | 2.9 | 0.58 2.25 | 5.1 | 1.01 2.67 | 7.1 | 1.43 3.00 | 9.0 | 1.80 3.27 | 10.7 | 2.18 3.50 | 12.3 | 2.43

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

Fig. 1.2.

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

ii) Determine the gradient of the graph.

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

Extract:

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. V / V, V^2 / V^2, P / W: 1.00, 1.0, 0.214 1.71, 2.9, 0.58 2.25, 5.1, 1.011 2.67, 7.1, 1.43 3.00, 9.0, 1.80 3.27, 10.7, 2.176 3.50, 12.3, 2.43

From part (b): R from graph (gradient) = 5.05 Ω (R is the reciprocal of the gradient, R = V^2/P).

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.

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).

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

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).

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.

Extract:

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.

Explain how these heaters can be made more efficient.

Extract:

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. Heater A: Current, I = 17 A, Potential difference, V = 90 V

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 2*I *respectively.

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