Question

A potential difference of 220 V is maintained across 12000 Ω rheostat. Then voltmeter V has a resistance of 6000 Ω and point C is at one fourth the distance from a to b. Then the reading of voltmeter is ______.

विकल्प

• 45 volt

• 40 volt

• 60 volt

• 30 volt

Answer 1

A potential difference of 220 V is maintained across 12000 Ω rheostat. Then voltmeter V has a resistance of 6000 Ω and point C is at one fourth the distance from a to b. Then the reading of voltmeter is 40 volt.

Explanation:

Resistance R = `1/4 "R" = 12000/4 = 3000` parallel

`1/"R"_"p" = 1/"R"_"ac" + 1/"R"_"V"`

`= 1/3000 + 1/6000 = 1/2000; "R"_"p" = 2000 Omega`

This is in series with R_bc.

R_bc = R - R_ac = 12000 - 3000Ω = 9000 Ω

R_eq = R_p + R_bc = 9000 + 2000 = 11000 Ω.

The current in the circuit 

I = `220/11000` = 0.02 A

The reading of the voltmeter is the potential drop across R_p, V = 0.02 × 2000 = 40 V