Question

A galvanometer having a resistance of 20 Ω and 30 Ω division 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 volt, is ______.

Options

• 100 Ω

• 120 Ω

• 80 Ω

• 125 Ω

Answer 1

A galvanometer having a resistance of 20 Ω and 30 Ω division 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 volt, is 80 Ω.

Explanation:

Deflection current = lg_max = nxk = 0.005 × 30

Where, n = Number of divisions = 30 and k = 0.005 amp/ division

= 15 × 10^-2 = 0.15

v = I_g [20 + R]

⇒ 15 = 0.15 [20 + R]

⇒ 100 = 20 + R

⇒ R = 80Ω