1.The Wheatstone bridge is a particularly accurate method for measuring resistance because


(a) it is a ‘null-deflection’ method, so the indicating instrument accuracy does not affect the result

(b) three resistors are required as well as that to be measured

(c) a sensitive centre-zero galvanometer

(d) the slide-wire method can be used

2. The Murray-loop test can be used to

(a) measure the sweetness of a sugar solution

(b) find the position of a cable fault (c) measure the combined resistance of both cores of a two-core cable

(d) take measurements from which cable length can be calculated

3. A megohm-meter used to test insulation resistance must apply a direct voltage so that

(a) it is safer to use

(b) the reading is in megohms rather than in kilohms

(c) the scale is linear

(d) it measures insulation resistance rather than insulation impedance.

4. Because of the heavy current it carries, the earth-fault-loop tester must not

be connected for more than

(a) 1 s (b) 50 ms (c) 30 ms (d) 40 ms