A3. This question is about testing an electrical circuit.

The diagram below shows an electrical circuit consisting of four identical resistors RA, RB, RC, and RD. The resistance of each resistor is 10 kΩ.















(a) Commercial resistors sometimes fail in one of two ways. They can go “open-circuit” in which the resistance of the resistor becomes infinite or they can go “short-circuit in which the resistance becomes zero.

In order to test the circuit a technician connects a high resistance voltmeter between the terminals X and Y
and applies a potential difference of 6 V across the resistor RA.
(i) What voltage will the voltmeter read if all the resistors are functioning normally?
(ii) What would the voltmeter read if either resistor RB or RD were to short-circuit?
(iii) If the electrician were to note a reading on the voltmeter that suggested either RB or RD had short-circuited how could he test which one of these had in fact short-circuited using only the voltmeter?

(b) Identify a possible fault with the circuit that would produce a reading of 6 V on the voltmeter when it is
connected between X and Y.