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A 35V dc supply is connected across a resistance of 600 ohm in series with an unknown resistance Rx. A voltmeter having a resistance of 1·2 k-ohm is connected across 600 ohm resistance and reads 5V. The value of resistance Rx will be:
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- 120 ohm
- 400 ohm
- 1·8 k-ohm
- 2·4 k-ohm
- 120 ohm
Correct Option: D
From the given information we can make the circuit arrangement given below:
Let current I is flowing in the circuit.
Here,
| I = | |
| Effective resistance offered by the voltmeter |
or
| I = | |
| 600 | | 1200 |
or
| I = | = | = | Amp | |||
| 720000/1800 | 400 | 80 |
Now, Rx = 35 – 5/I
or
| Rx = | |
| 1/80 |
or
Rx = 2400
or
Rx = 2·4 kΩ.
