# A Long Solenoid with 15 Turns per Cm Has a Small Loop of Area 2.0 cm^2 PlacedInside the Solenoid Normal to Its Axis. - Physics

Numerical

A long solenoid with 15 turns per cm has a small loop of area 2.0 cmplaced inside the solenoid normal to its axis. If the current carried by the solenoid changes steadily from 2.0 A to 4.0 A in 0.1 s, what is the induced emf in the loop while the current is changing?

#### Solution

Number of turns on the solenoid = 15 turns/cm = 1500 turns/m

Number of turns per unit length, n = 1500 turns

The solenoid has a small loop of area, A = 2.0 cm2 = 2 × 10−4 m2

Current carried by the solenoid changes from 2 A to 4 A.

∴ Change in current in the solenoid, di = 4 − 2 = 2 A

Change in time, dt = 0.1 s

Induced emf in the solenoid is given by Faraday’s law as:

"e" = ("d"phi)/("dt") ........(1)

Where,

phi = Induced flux through the small loop = BA ...........(2)

B = Magnetic field = mu_0"ni" .....(3)

μ0 = Permeability of free space

= 4π × 10−7 H/m

Hence, equation (i) reduces to:

"e" = "d"/("dt")("BA")

= "A"mu_0"n" xx (("di")/("dt"))

= 2 xx 10^-4 xx 4pi xx 10^-7 xx 1500 xx 2/0.1

= 7.54 xx 10^-6  "V"

Hence, the induced voltage in the loop is 7.54 xx 10^-6  "V".

Concept: Inductance - Mutual Inductance
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#### APPEARS IN

NCERT Class 12 Physics Textbook
Chapter 6 Electromagnetic Induction
Exercise | Q 3 | Page 230
NCERT Physics Part 1 and 2 Class 12
Chapter 6 Electromagnetic Induction
Exercise | Q 6.3 | Page 230

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