New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
CHAPTER 5 ELECTROMAGNETIC INDUCTION
1
Quick Summary on Previous Concepts
Electrostatics
Magnetostatics
Electromagnetic Induction
2
Cases of Changing Magnetic Field
Changing Field Strength in a Loop
A Loop Leaving a Magnetic Field
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
3
Explanation: Conductor Cutting Magnetic Field Lines
Induced EMF for Conductor Cutting B-field Lines
Fleming’s Right Hand Rule
4
Easy Summary of Electromagnetic Induction
Faraday’s Law of Electromagnetic Induction (Strength of Induced EMF)
Lenz’s Law of Electromagnetic Induction (Strength of Induced EMF)
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
[HKCEE] [Induced Current]
A metal ring is released and falls vertically around a magnet as shown above. Draw
the direction of induced current at positions X and Y.
[HKCEE] [Right Hand Rule]
In the above diagram, a metal rod is placed inside a magnetic field pointing into the paper. In which
direction should the rod be moved in order to produce an induced current as shown in the diagram?
[HKCEE] [Lenz’s Law]
A bar magnet is placed near a solenoid. Which of the following correctly shows the direction of the
induced current in the solenoid?
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
[HKALE] [Induced EMF]
In the above figure, when the metal rod PQ moves with constant velocity across a uniform magnetic field,
a p.d. is induced across the rod. Which of the following statements is/are correct?
(1)
(2)
(3)
The magnitude of the p.d. depends on the length of the rod.
Q is at a higher potential than P.
A force is acting on the rod to oppose its motion.
A. (1), (2) and (3)
D. (1) only
B. (1) and (2) only
E. (3) only
C. (2) and (3) only
[HKALE] [Faraday’s Law]
The figure shows a rectangular coil PQRS moving from left to right with a uniform speed across an
insulated metal wire in the plane of the coil. The wire carries a steady current I. Which of the following
gives the correct sequence for the direction if the current induced in the coil PQRS?
A. Clockwise and then anticlockwise
B. Anticlockwise and then clockwise
C. Clockwise, then anticlockwise and finally clockwise again
D. Anticlockwise, then clockwise and finally anticlockwise again
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
5
Mathematical Description of Induced EMF [FX only]
Magnetic Flux, Flux Density and Flux Linkage
Faraday’s Law
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
[HKALE] [Cutting Field Lines] [FX only]
A metal rod of length l is inclined at 60o to rail PQ as shown. It is moved across a uniform magnetic field
along the direction of the two horizontal rails PQ and RS. If the rod moves with a uniform velocity v and
the flux density of the field is B, the e.m.f. induced in the rod is
A.
Blv
2
B.
Blv
C.
2 Blv
3
D.
3Blv
2
[HKALE] [Faraday’s Law] [FX only]
A solenoid of n1 turns per metre and cross-sectional area A1 carries a current I. It is inserted into the core
of another larger solenoid of N 2 turns and cross-sectional area A2 . If the current in the smaller solenoid
drops uniformly to zero in time t, what is the e.m.f. induced in the larger solenoid?
A.
D.
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2µ0 n1 IA1 N 2
t
µ0 n1 IA2 N 2
t
B.
E.
2µ0 n1IA2 N 2
t
µ0 n1IA1 N 2
t
C.
µ0 n1IA1 A2
t
New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
6
Application of Electromagnetic Induction: Generator
Induced EMF in rotating coil
Simple A.C. Generator
Draw the graph of induced current against time:
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New Senior Secondary Physics Compulsory:
Compulsory Electricity and Magnetism
Chapter 5 Electromagnetic Induction
Simple D.C. Generator
Factors Affecting Induced EMF
1.
2.
3.
4.
5.
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
7
Eddy Current
Concept
8
Application of Induced EMF
Moving Coil Microphone
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New Senior Secondary Physics Compulsory: Electricity and Magnetism
Chapter 5 Electromagnetic Induction
Induction Cooker
FINAL REMARKS
Electromagnetic induction is the linkage between electricity and magnetism. We found that a changing magnetic
field can lead to an induced electric field. A charge that moves along the electric field can acquire an amount of
energy (per unit charge) which is called the induced EMF. To be precise, the changing magnetic field is
quantified by the changing magnetic flux over through a coil. A changing magnetic flux can be caused by (i)
changing magnetic field strength, (ii) changing area of the loop or (iii) changing angle between the area and the B
field. The rate of change of magnetic flux determines the induced EMF, the mathematical statement is given by
the Faraday’s law.
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