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Methods of Production of Induced Emf: Explanation 1: Using Faraday's Law

1) There are three main methods to induce electromagnetic force (emf) in a coil: changing the magnetic field strength, changing the shape or area of the coil, and rotating the coil in a magnetic field to change the angle between the field and coil area. 2) Motional electromagnetic force (emf) is generated by moving a conductor through a magnetic field. As a conductor moves perpendicular to a magnetic field, charges in the conductor will experience a force and induce a current. 3) Faraday's law and the Lorentz force law can both be used to explain motional emf. Charges moving through a magnetic field experience a force, and the work done moving the charges induces an emf

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Nishita Sah
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730 views3 pages

Methods of Production of Induced Emf: Explanation 1: Using Faraday's Law

1) There are three main methods to induce electromagnetic force (emf) in a coil: changing the magnetic field strength, changing the shape or area of the coil, and rotating the coil in a magnetic field to change the angle between the field and coil area. 2) Motional electromagnetic force (emf) is generated by moving a conductor through a magnetic field. As a conductor moves perpendicular to a magnetic field, charges in the conductor will experience a force and induce a current. 3) Faraday's law and the Lorentz force law can both be used to explain motional emf. Charges moving through a magnetic field experience a force, and the work done moving the charges induces an emf

Uploaded by

Nishita Sah
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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XII –6.

PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3

METHODS OF PRODUCTION OF INDUCED EMF

Flux can be varied by varying B, A or θ. Therefore, emf can be induced by


1. Changing B (e.g. time varying field)
2. Changing the shape of the coil (area changes)
3. Rotating coil in a magnetic field so that angle θ between B and A changes
6.6 MOTIONAL ELECTROMOTIVE FORCE
The emf generated by moving a conductor
in a magnetic field i.e. by changing the flux
in the circuit is called motional EMF.
In the figure, there is a rectangular
conductor PQRS kept in a magnetic field B,
in which arm PQ of length L is free to
move. The rod PQ is moved towards left
with a constant velocity v. Assume that
there is no loss of energy due to friction
Explanation 1: Using Faraday’s Law

XII –6. PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3 KULDIP THAKUR


XII –6. PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3

Explanation 2: Using Lorentz force


Consider a charge q in the conductor PQ. As PQ moves towards the left with
velocity v, the charge will also move with same velocity. As the charge is
moving in a magnetic field, it will experience a force F = qvB towards Q. All
like charges will experience the same force in the same direction. The work
done in moving a charge from P to Q

Note: General formula

EMF induced in a stationary conductor kept in a varying magnetic field:


In case of stationary conductor, the force on its charges will be

Since v=0, the force must be due to E. therefore, to explain the induction of
current we must assume that a time varying magnetic field generates an 6.28
× 10–5 VElectric field. But, the electric field due to static charges and that due
to varying magnetic field have different properties.
Motional EMF in rotation (PYQ 2012)
Example 6.6 A metallic rod of 1 m length is rotated with a frequency of 50
rev/s, with one end hinged at the centre and the other end at the
circumference of a circular metallic ring of radius 1 m, about an axis passing
through the centre and perpendicular to the plane of the ring (Fig. 6.11). A
constant and uniform magnetic field of 1 T parallel to the axis is present
everywhere. What is the emf between the centre and the metallic ring ?

XII –6. PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3 KULDIP THAKUR


XII –6. PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3

Example 6.7 A wheel with 10 metallic spokes each 0.5 m long is rotated with
a speed of 120 rev/min in a plane normal to the horizontal component of
earth’s magnetic field HE at a place. If HE = 0.4 G at the place, what is the
induced emf between the axle and the rim of the wheel? Note that 1 G = 10–4 T
(Answer 6.28 × 10–5 V)

XII –6. PHYSICS ELECTROMAGNETIC INDUCTION LECTURE: 3 KULDIP THAKUR

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