Q 12-04-224JEE MainJEE Main 2019 (12 Apr, Shift 1)Medium
A galvanometer of resistance $100\ \Omega$ has $50$ divisions on its scale and has sensitivity of $20\ \mu$A/division. It is to be converted to a voltmeter with three ranges, of $0$–$2$ V, $0$–$10$ V and $0$–$20$ V. The appropriate circuit to do so is:
Answer: (D) see figure
Full-scale current: $I_g = 50\times20\ \mu\text{A} = 1$ mA.
Total resistance needed: $2000\ \Omega$ for $2$ V, $10000\ \Omega$ for $10$ V and $20000\ \Omega$ for $20$ V. With the resistors in series and the taps after $R_1$, $R_2$, $R_3$:
$$R_1 = 2000 - 100 = 1900\ \Omega,\quad R_2 = 10000 - 2000 = 8000\ \Omega,\quad R_3 = 20000 - 10000 = 10000\ \Omega$$
Solution by Sreeraj P, M.Sc Physics