JEE Main On 16 April 2018 Question 22
Question: A galvanometer with its coil resistance $ 25\Omega $ requires a current of 1mA for its full deflection. In order to construct an ammeter to read up to a current of 2A, the approximate value of the shunt resistance should be [JEE Main 16-4-2018]
Options:
A) $ 2.5\times {10^{-2}}\Omega $
B) $ 1.25\times {10^{-3}}\Omega $
C) $ 2.5\times {10^{-3}}\Omega $
D) $ 1.25\times {10^{-2}}\Omega $
Show Answer
Answer:
Correct Answer: D
Solution:
Formula: $ S={G^*}I/(I-Ig) $
where S= shunt resistance ,
(I-Ig)= current through the shunt resistance ,
I=Current in the circuit.
Here, galvanometer resistance, G= 25 ohm ;
Ig= 0.001 A , I= 2A $ s=({25^*}0.0001)/(2-0.001) $
$ =1.25\times {10^{-3}}\Omega $
A shunt resistance of $ 1.25\times {10^{-2}}\Omega $ must be connected to make the galvanometer in the range of 0 to 2A
