JEE MainPhysicsCurrent ElectricityMCQ+4 / −1
A moving coil galvanometer allows a full scale current of 10–4 A. A series resistance of 2 M is required to convert the above galvanometer into a voltmeter of range 0-5 V. Therefore the value of shunt resistance required to convert the above galvanometer into an ammeter of range 0.10 mA is :
- A200
- B500
- C100
- DNone of the options are correct
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Correct answer: D
- Given data
- Full scale current of galvanometer:
- Series resistance required to make voltmeter of range to :
We first find the resistance of the galvanometer, .
- Find galvanometer resistance
For a voltmeter made from a galvanometer:
Substitute the values:
So,
Thus,
This is physically impossible because resistance cannot be negative.
So the given data are inconsistent.
- Check the ammeter conversion condition
Desired ammeter range:
But this is exactly equal to the galvanometer full scale current:
Hence, to convert the galvanometer into an ammeter of range , no shunt is needed at all.
That means:
because the galvanometer itself already measures up to .
- Evaluate options
- A: — incorrect
- B: — incorrect
- C: — incorrect
- D: None of the options are correct — correct
- Final answer
The required shunt resistance is not any finite value from the options; effectively no shunt is required.
So the correct option is:
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