Basic Electricity Paper 2 , May/June 2014
 Questions: 1 2 3 4 5 6 7 Main
Weakness/Remedies
Strength

Question 4
1. Explain damping as applied to electrical measuring instruments.

(b)   State two advantages of a digital meter over an analogue meter.
(c) A moving-coil instrument has a resistance of 10 Ω with a full-scale
deflection (f.s.d.) of 8 mA. With the aid of a sketch, calculate the value of

a multiplier that will enable it read up to 100 V
_____________________________________________________________________________________________________
Observation

(a)  In an electrical measuring instrument, the combination of the inertia of the moving system and the controlling torque of the spiral springs or of gravity gives the moving system a natural frequency of oscillation called damping.
(b) (i) Digital meter has high impedance hence less error
(ii)Digital meter can be read by an inexperienced person from a far

(c)V = Va + Vm = Ira + IRm
100 = 0.008 x 10 + 0.008Rm
100 – 0.08 = 0.008Rm
Rm=  = 12490 = 12.49 kΩ
The question was on Measuring Instruments. It was very popular with the candidates. Those who attempted this question did better in part (c) than they did in parts (a) and (b).