Current, Potential Difference, Resistance & Power (Edexcel International AS Physics): Structured Questions

Two resistors of resistance $R_1$ and $R_2$ are connected in parallel in a circuit.

Derive a formula for the total resistance $R_{\mathrm{T}}$ of the combination.

The diagram shows a combination of five resistors, M, N, O, P and Q. Each resistor has a resistance of 5.0 Ω.

i) Show that the resistance between points A and B is about 3 Ω.

(3)

ii) A student is told to modify the combination of resistors so that the combined resistance between A and B is greater than 5.0 Ω. She cannot change the arrangement of the resistors, but she can replace one of the 5.0 Ω resistors with a 20.0 Ω resistor.

Explain, without further calculations, which of the five resistors should be replaced.

(2)

The circuit diagram shows three identical resistors and two switches, X and Y.

The battery has negligible internal resistance.

Each resistor consists of a wire of diameter 0.181 mm and length 55.0 cm. At room temperature, the resistivity of the wire is 1.10 × 10⁻⁶ Ω m.

Show that the resistance of one resistor at room temperature is about 24 Ω.

A student suggests that the maximum power output from the resistors in this circuit will be greater than 12 W.

Assess whether the student’s suggestion is correct.

Switch X was open and switch Y was closed.

i) Calculate the number of conduction electrons passing through the resistor every second immediately after switch Y was closed.

Number of electrons = ............................(3)

ii) After switch Y had been closed for a few minutes, the power dissipated by the resistor decreased.

Explain why.

(3)

A student set up the circuit shown.

Calculate the number of electrons passing point X each second.

Number of electrons in one second = ..............................

Another resistor, Y, is added to the circuit as shown.

The student wrote the following statement.

Evaluate the student’s statement.

A bicycle lighting system contains a battery with an electromotive force (e.m.f.) of 6.0 V and an internal resistance of 0.50 Ω.

State what is meant by the e.m.f. of the battery.

The lighting system consists of two lamps of resistance $R_1$ and $R_2$ connected in parallel.

Derive an equation for the combined resistance $R_T$ of two lamps.

The circuit diagram shows the battery connected to the front and rear lamps.

Calculate the power dissipated in the front lamp.

A third lamp is connected in parallel with the front and rear lamps.

Without further calculation, explain what happens to the current from the battery.