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Physics > Electromagnetic Induction > Flashcards

Electromagnetic Induction Flashcards

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1
Q

Who discovered electromagnetic induction?

A

Micheal Faraday in 1831 discovered when magnetic flux linking a conductor changes, emf is induced in the conductor.

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2
Q

What is flux linkages?

A

Product of the number of turns of coil and magnetic flux linking the coil.
Flux linkages = N × Flux

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3
Q

Magnitude of induced emf depends upon?

A

Rate of change of flux linkages. By Faraday’s law of induction.

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4
Q

Direction of induced emf is given by?

A

Lenz’s law. (by German Scientist Heinrich Lenz in 1834)
emf = - N. del flux/ del T
here negative sign represents Lenz’s law

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5
Q

Faraday and Lenz law ?

A

The magnitude of induced emf is given by Faraday’s law and direction of induced emf is Lenz’s law.

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6
Q

Inertial Seiosmometer?

A

Seismometer based on Newton’s first law. Consists of mass spring system to detect vibrations in Earth’s surface.

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7
Q

Electromagnetic seiosmometer?

A

Magnet is used as inertial mass itself commercially.

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8
Q

Law of conservation of energy?

A

Lenz’s law

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9
Q

Generator construction

A

A coil loop
2 carbon brushes
2 copper slip rings
A horseshoe magnet

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10
Q

The direction of emf and induced current changes how often in ac generator?

A

Direction changes every half revolution.
OR
Current alternates in direction once in one cycle.

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11
Q

How many times the current produced by AC generator reverses its direction in 1 second?
(ac frequency is 50 Hz)

A

Coil is rotated at the rate of 50 revolutions per second. Since in one revolution of coil, the current reverses its direction once , So in 50 revolutions of coil the current reverses its direction 50 Times.
f times per second.

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12
Q

When is ac generated max and min?

A

when coil loop in vertical in magnetic field, minimum emf is produced.
when coil loop in horizontal in magnetic field, max emf is produced.

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13
Q

Principle of ac generator?

A

Faraday’s law of induction

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14
Q

principle of transformer?

A

mutual induction

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15
Q

Actual practice Ac generator?

A
  1. Iron cylinder, number of coils wound on it, assemblage is called ARMATURE.
  2. Electromagnet
  3. Armature is rotated by fuel engine or turbine run by waterfall
  4. Commercially, FIELD MAGNET is rotated around stationary armature.
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16
Q

What is a power transforming device?

A

A transformer.

Changes given ac emf into larger or smaller ac emf.

17
Q

Which quantity remains constant in transformer?

A

Frequency, power

18
Q

Construction of transformer?

A

Laminated Iron core

2 Copper wires

19
Q

Power is transferred by transformer via?

A

By means of changing flux

20
Q

Voltage is stepped up at generating power stations up to ?

A

several thousand volts

21
Q

Voltage stepdown for ringing a bell or operating a transistor radio?

A

From 250V to 9V

22
Q

Transformers in TV and radio receivers?

A

Transformers with several secondaries becauses several different voltages are required.

23
Q

To prevent power loss what is used?

A
  1. Soft iron core to reduce hysterises, use materials with small hysterises loops.
  2. lamination, with insulation in between layers of lamination to reduce eddy current
  3. resistance of coils is kept minimum
  4. flux coupling between coils should be maximum
24
Q

Direction of eddy currents?

A

Perpendicular to flux

25
Q

Power losses ?

A
  1. eddy currents

2. hysterises loss

26
Q

When high voltage is required?
when high current is required?
step down or step up transformer is used?

A

Step up for high voltage

step down for high current

27
Q

What is flux leakage?

How to reduce?

A

Not all flux due to primary passes through secondary.
some is lost due to poor design or air gaps in the core.
it can be reduced by winding coils over one another.

28
Q

Voltage boost up at power plants?

A

40,000 volts

29
Q

Long, thick transmission lines are made up of?

A

Aluminum or copper, because they have low resistance.

30
Q

Household voltages

A

220 V for larger appliances like stoves, clothes dryers

110 V for lights, TV etc.

31
Q

Units of flux

Maxwell is smaller unit than weber

A 
1 Wb = (kg.m2)/(s2.A)
=V.s
=H.A
=T.m2
=JA
=10^8M.x
32
Q

Device in which induced emf is statically induced?

A

Transformer

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