Q. In a copper voltmeter , if the current ($I)$ and time $(t)$ variations of the type as shown in figure, the mass deposited in 30 min is [Atomic weight of copper is 63.5 and Faraday constant is 96500 C per g equivalent]
A) 0.078 g
B) 0.054 g
C) 0.039 g
D) 0.0195 g
Explanation
(c) Charge flowing in 30 min,
$q =$ area under graph
$= \left\lbrack \frac{0.1 \times 10}{2} + 0.1 \times 10 + \frac{0.1 \times 10}{2} \right\rbrack \times 60$
$\ = 120$C
$\therefore m = zq = \frac{M}{F}q = \frac{31.5}{96500} \times 120 = 0.039$ g
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.