Question

The scale of a galvanometer of resistance 100 Ω contains 25 divisions. It gives a deflection of one division on passing a current of 4 × 10^–4A. The resistance in ohms to be added to it, so that it may become a voltmeter of range 2.5 volt is

• A. 100
• B. 150
• C. 250
• D. 300

Answer 1

Answer: (B)

150

Answer 2

Current sensitivity of galvanometer = 4 × 10^–4 Amp/div.

So full scale deflection current (i_g) = Current sensitivity × Total number of division = 4 × 10^–4 × 25 = 10^–2 A

To convert galvanometer in to voltmeter, resistance to be put in series is $R = \frac{V}{i_{g}} - G = \frac{2.5}{10^{- 2}} - 100 = 150\Omega$