Q. 524.0( 4 Votes )
A voltmeter coil
Potential Difference (V) across a resistor of resistance R when current I passes through it is given by Ohm’s law:
It consists of a galvanometer coil in parallel with a stunt resistance.
Kirchhoff’s junction rule:
The sum of currents entering a junction is equal to the sum of currents leaving it.
The given voltmeter looks like this:
The maximum potential difference that can be measured is ,and let the current through the voltmeter for maximum deflection be .
Note that the coil (r) and the other resistor (R) are in series.
(Note that 1kΩ = 1000Ω )
Now, using Ohm’s law,
The ammeter we want looks like the following diagram:
The maximum current that can be measured is .
From our previous calculations we know that the current through the coil for maximum deflection is .
Note that the shunt resistance (rs) and the coil (r) are parallel in an ammeter.
By Kirchhoff’s junction rule,
Using Ohm’s law, we have
As rs and r are in parallel, the potential difference across them is the same.
Hence, the shunt resistance is 0.251Ω.
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