GATE EE 2005 Electrical and Electronic Measurements Solution Q 7 - Grad Plus
GATE EE 2005 Electrical and Electronic Measurements Solution

GATE EE 2005 Electrical and Electronic Measurements Solution Q 7

A 1000 V DC supply has two 1-core cables as its positive and negative leads: their insulation resistances to earth are 4 MΩ and 6 MΩ, respectively, as shown in the figure. A voltmeter with a resistance of 50 kΩ is used to measure the insulation of the cable. When connected between the positive core and earth, the voltmeter reads___

a) 8V

b) 16V 

c) 24 V 

d) 40 V 

Ans. (a)

Explanation-

Effective resistance between A and B ,

RAB = Rv || 4 MΩ

Rv=50 k Ω = 0.05 M Ω

RAB=0.05 || 4 MΩ

Hence, RAB ≈ 0.05 MΩ

RAC= RAB+ RBC

∴ RAC=0.05 + 6 = 6.05 MΩ

I=\frac{1000}{R_{AC}}=\frac{1000}{6.05}\; \mu A

Voltmeter reads,

IR_{AB}=\frac{1000}{6.05}\times 10^{-6}\times 0.05 \times 10^{-6}= 8 V
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