Question

A range of galavanometer is '$V$', when $50\Omega$ resistance is connected in series. Its range gets doubled when $500\Omega$ resistance is connected in series. Galvanometer resistance is

• A. $100\Omega$
• B. $200\Omega$
• C. $300\Omega$
• D. $400\Omega$

Answer 1

The correct option is D $400\Omega$

Case 1: $R_s=50\Omega$

Using $V=I_g(R_g+R_s)$

$\therefore$ $V=I_g(R_g+50)$ ....(1)

Now the range is doubled i.e. $2V$ when $R_s=500\Omega$

$\therefore$ $2V=I_g(R_g+500)$ ....(2)

Dividing (2) and (1) we get $2=\frac{R_g+500}{R_g+50}$

Or $2R_g+100=R_g+500$

$⟹$ $R_g=400\Omega$