Question

The reading of the ideal voltmeter connected across 400 resistance is 20 V then find out the value of resistance R

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Answer 1

Answer:

r=1200 ohm

Here, it is a closed circuit with resistors connected in series so current will be same. Current in the circuit is v/R = 20/400 = 0.05A .

potential difference across R is 60V(since total voltage is 80V)

so r = v/i = 60/0.05 = 1200 ohm

Answer 2

Given info : The reading of the ideal voltmeter connected across 400 Ω is 20 V as shown in figure.

To find : The value of resistance R is ..

solution : current through the resistance 400Ω is given by, I = V/R

= 20 volts/400 Ω

= 1/20 A

= 0.05 A ...(1)

as you see, resistors R and 400 Ω are joined in parallel combination so, current through each will be same.

now, equivalent resistance = (R + 400)

potential across it is 80 volts.

from Ohm's law, V = IR

so, 80 volts = 0.05 × (R + 400) [ from eq (1).]

⇒80 × 20 = R + 400

⇒1600 = R + 400

⇒R = 1200 Ω

Therefore the value of resistance R is 1200 Ω

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