Lecture Notes :-
Q. A galvanometer with a full scale current of 10mA has a resistance of 1000Ω. The multiplying power (the ratio of measured current to
galvanometer current) of 100Ω shunt with this galvanometer is [2004]
(a) 110
(b) 100
(c) 11
(d) 10
Ans.
Given :- Ifs = Im = 10 mA
Rm = 1000 Ω
Rsh = 100 Ω
m= ?
Solution :- The formula for calculating multiplying factor is given by,
m= measured current / galvanometer current = I/Im
Ish Rsh = Im Rm —-(i)
I = Im + Ish
Ish = I – Im
(I-Im) Rsh = Im Rm
IRsh – Im Rsh = Im Rm
IRsh = Im Rsh + Im Rm
IRsh = Im (Rsh + Rm)
\frac{I}{I_{m}}=\frac{R_{sh}+R_{m}}{R_{sh}}=m m=\frac{100+1000}{100}=11Therefore, option (c) is the correct answer.