Test Index

NCERT Class XII Chapter
Electromagnetic Induction
Questions With Solutions

© examsnet.com
Question : 15
Total: 17
An air cored solenoid with length 30 cm, area of cross-section 25 cm2 and number of turns 500, carries a current of 2.5 A. The current is suddenly switched off in a brief time of 10–3s. How much is the average back emf induced across the ends of the open switch in the circuit? Ignore the variation in magnetic field near the ends of the solenoid.
Solution:  

Magnetic field inside solenoid
B =
µ0NI
l
Flux linked with solenoid
ϕi = BAN =
µ0N2AI
l
 ... (1)
Initial flux,
ϕi =
4π×10−7×(500)2×25×10−4×2.5
30×10−2
Wb
ϕi = 6.54 × 10−3 Wb
Final flux, ϕf = 0 [I = 0]
Average back emf
eav = -
(ϕf−ϕi)
t
 = - [
0−6.54×10−3
10−3
] = 6.54 V
© examsnet.com
Go to Question:
Prev Question
Next Question