Question

A galvanometer having a resistance of $20 \, \Omega $ and $30$ divisions on both sides has figure of merit $0.005 \, $ ampere/division. The resistance that should be connected in series such that it can be used as a voltmeter upto $15$ $V$ , is:

• A. $120 \, \Omega $
• B. $100 \, \Omega $
• C. $80 \, \Omega $
• D. $125 \, \Omega $

Answer 1

Answer: (C)

Current for full scale deflection $=0.005\times 30=0.150 \, A$
Voltage for full scale deflection $=0.150\times 20 \, V$
$=3.0 \, V$
Resistance required to be connected in series $=\left(\frac{15}{3} - 1\right) \, 20 \, \Omega $
$=80 \, \Omega $