Question

A long solenoid of radius 2 cm has 100 turns/cm and is surrounded by a 100 turn coil of radius 4 cm having a total resistance 20W. If current changes from 5 A to – 5A, find the charge through galvanometer.

• A. Zero
• B. 800 µc
• C. 400 µC
• D. 600 µC

Answer 1

Answer: (B)

800 µc

Answer 2

f = Bpr ² e =$\frac{d\varphi}{dt}$= Npr²$\frac{dB}{dt}$

= Npr²m₀n$\frac{di}{dt}$

I =$\frac{\varepsilon}{R}$and DQ = IDt =$\frac{N\pi r^{2}\mu_{0}n}{R}$Dt

DQ =$\frac{100 \times \pi \times (2 \times 10^{- 2})^{2} \times 10^{4} \times 4\pi \times 10^{- 7} \times 10}{20}$

= 8 × 10^–4c = 800 µC