An AC generator consists of a coil of 500 turns each having an area of 100 cm 2 in a uniform magnetic field of 2 × 10 - 2 Wb / m 2 . If the speed of rotation is 100 rotations per second, what is the value of maximum e.m.f. induced in the coil?

We know that the maximum e.m.f. is given by, e o = N A B ω where N is the number of turns in the coil, A is the area enclosed by each turn of the coil and B is the magnetic field. Given: N = 500 , A = 1 × 10 - 2 m 2 , B = 2 × 10 - 2 Wb / m 2 , ν = 100 rps . Putting the values in the formula, e o = N A B ω = N A B ( 2 π ν ) e o = 500 × 10 - 2 × 2 × 10 - 2 × 2 × 3 . 14 × 100 ⇒ 62 . 8 V

What are Eddy currents? Describe any three uses of it.

Eddy currents are the currents induced in a metallic plate when it is kept in a time-varying magnetic field or when metallic plate moves in a magnetic field. Magnetic flux linked with the plate changes and so the induced current is set up. Eddy currents are sometimes so strong, that metallic plate becomes red hot. Uses of Eddy currents : Magnetic breaking in train : In some electrically powered trains, strong electromagnets are situated in the train, just above the rails. When electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train. As there are no mechanical linkages, therefore, the braking action is smooth. Induction furnace : It is used to produce high temperatures which are utilised in preparing alloys by melting the constituent metals. A high frequency alternating current is passed through a coil which surrounds the constituent metals. The large eddy currents generated in the metals produce high temperatures sufficient to melt the metals. Electric power meters : This is a metal disc which rotates due to eddy currents developed in the disc, by magnetic fields produced by alternating current.

Describe the ways in which Eddy currents are used to advantage.

When bulk pieces of conductors are subjected to changing magnetic flux, induced currents produced in them are called eddy currents. The eddy currents can be used to advantage in the following ways: (i) Magnetic braking in trains: Strong electromagnets are situated above the rails in electrically powered trains. When electromagnets are activated, the eddy currents induced in the rails oppose the motion of the train. As there are no mechanical linkages, the braking effect is smooth. (ii) Electromagnetic damping: Moving coil galvanometers have a fixed core made of nonmagnetic metallic material. When the coil oscillates, the eddy currents generated in the core oppose the motion and bring the coil to rest quickly. (iii) Induction furnace: It can be used to produce high temperatures and can be utilised to prepare alloys by melting the constituent metals. A high frequency alternating current is passed through a coil which surrounds the metal to be melted. The eddy currents generated in the metals produce high temperatures sufficient to melt. (iv) Electric power meters: A metal disc is present inside it. Electric currents are induced in it, and it rotates in a magnetic field induced by the alternating current in the coil.

EASY

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IMPORTANT

Earn 100

What is meant by self induction? Explain the phenomenon self induction through an experiment and find out self inductance of solenoid?

Important Questions on Electromagnetic Induction

MEDIUM

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IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 95

Explain the concept of self induction and mutual induction. Hence, define the coefficient of self induction and mutual induction. Write S.I. unit and dimensions of coefficient of self induction and mutual induction.

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12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 96

A thin wire ring of radius

a

and resistance

r

is located inside a long solenoid so that their axes coincide. The length of the solenoid is equal to

I

, its cross-sectional radius to

b

. At a certain moment the solenoid was connected to a source of a constant voltage

V

. The total resistance of the circuit is equal to

R

. Assuming the inductance of the ring to be negligible, find the maximum value of the radial force acting per unit length of the ring.

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 97

Find the inductance of a solenoid of length

l

whose winding is made of copper wire of mass

m

. The winding resistance is equal to

R

. The solenoid diameter is considerably less than its length.

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 98

A current

I_{0} = 1.9 A

flows in a long closed solenoid. The wire it is wound of is in a superconducting state. Find the current flowing in the solenoid, when the length of the solenoid is increased by

η = 5 %

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 99

Two thin concentric wires shaped as circles with radii

a

and

b

lie in the same plane. Allowing for

a ≪ b,

find,
(a) their mutual inductance,
(b) the magnetic flux through the surface enclosed by the outside wire, when the inside wire carries a current

I

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 100

What are the values of the self-induced $emf$ in the circuit of the previous problem at the times indicated therein?

Previous problem: An $L R$ circuit has $L = 1.0 H$ and $R = 20 Ω .$ It is connected across an $e m f$ of $2.0 V$ at $t = 0$ . Find $\frac{d i}{d t}$ at $(a) t = 100 ms, (b) t = 200 ms$ and $(c) t = 1.0 s .$

HARD

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 101

An AC generator consists of a coil of

500

turns each having an area of

100 {cm}^{2}

in a uniform magnetic field of

2 \times 10^{- 2} Wb / m^{2}

. If the speed of rotation is

100

rotations per second, what is the value of maximum e.m.f. induced in the coil?

EASY

12th Andhra Pradesh Board

IMPORTANT

Physics Crash Course (Based on Revised Syllabus-2023)>Chapter 9 - Electromagnetic Induction>Exercise>Q 102

What is the working principle of a thermal generator? Explain briefly.

What is meant by self induction? Explain the phenomenon self induction through an experiment and find out self inductance of solenoid?

Important Questions on Electromagnetic Induction

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