CH 10.

1
Electromagnetic
Induction
10th grade
Objectives

1. Explain Faraday and Henry experiment.

2. Compare between EMF and induced EMF.
3. List factors of induced EMF.
4. Calculate magnitude of EMF.
5. Indicate the direction of induced current.
Magnetic Field

Oersted Faraday and Henry

Magnetic field produces a current

Current produces magnetic field
When a current passes through When a wire moves through a
a wire, it produces a magnetic magnetic field, it induces a
field around the wire. current in the wire.

I produces B B produces I

Convert electricity 30 Convert magnetism

into magnetism P. 264 into electricity
 explain results of Faraday’s

Changing Magnetic Field and Henry’s experiment

Faraday’s and Henry’s Experiment

A wire formed a part of circuit and connected to galvanometer. Galvanometer: device
used to detect electric
when the wire is stationary or moves parallel to magnetic field
current and identify its
nothing happens (galvanometer reading is zero).
direction.

Magnetic force on
charges of wire is:
 explain results of Faraday’s

Changing Magnetic Field and Henry’s experiment

Faraday’s and Henry’s Experiment

When the wire is moved in a certain direction (upward)
and crossing the field, there is a current.

When the wire is moved in opposite direction (downward)

and crossing the field, there is a reversed current.

Notice:
to convert magnetism to electricity, it is required a wire in
a circuit, magnetic field (magnet) and motion.
 explain results of Faraday’s

Changing Magnetic Field and Henry’s experiment

The induced current in a circuit can be generated by two ways:

1. moving wire in stationary magnetic field. rel
a
mo tive
2. moving magnet while keeping wire stationary. tio
n

In other meaning: part of wire moves through and cuts 10

magnetic field, magnetic field moves past a stationary wire P. 253
or magnetic field changes around a wire.
 distinguish between

Induced Electromotive Force EMF and induced EMF

Electromotive Force (EMF): source of potential difference

that moves charges, it is produced by chemical reaction.
e.g., battery.

Induced Electromotive Force (EMF): source of potential

difference that moves charges, it is produced by a
changing of magnetic field. e.g., generator.

EMF is not a force, rather it is potential difference 𝐸𝑀𝐹 ≡ ∆ 𝑉

31
P. 264
 define electromagnetic

Induced Electromotive Force induction and induced

current

Electromagnetic Induction: process of generating current

through a wire in a circuit in changing magnetic field. ∆ 𝑉 =𝐸𝑀𝐹=𝐼𝑅
Induced Electromotive Force (EMF): source of potential
difference that moves charges, it is produced by a changing wire should be a
of magnetic field. e.g., generator. part of a circuit

Induced Current: is the current generating by changing

magnetic field. It requires an induced source.

The magnitude of induced current is calculated by Ohm’s law.

The direction of induced current in the same direction of EMF
 explain induced EMF

Induced Electromotive Force

When a wire in a circuit is moved in magnetic field, charges
experience a magnetic force.
This force moves positive charges on one end of wire and
negative charges on the other end.
Separation of charges produces an electric field which
produces potential difference or electromotive force (emf).
The electromotive force produces an induced electric
current, where both have the same direction. 𝐹 → 𝐸 →𝐸𝑀𝐹 →𝐼
All in the same direction
for positive charges
ΔV: potential difference across source or resistor
EMF: potential difference across source 24
EMF (induced): potential difference across a wire in magnetic field P. 264
 list factors of

Induced Electromotive Force induced EMF

Induced Electromotive Force (EMF): source of potential

difference that moves charges, it is produced by a
changing of magnetic field. e.g., generator.

Induced electromotive force can be calculated by:

𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃 EMF magnitude

EMF: electromotive force (V)

v: velocity of moving wire (m/s) E MF
L: length of moving wire (m) fact v,L, and B are directly
ors
B: magnetic field (T) proportional to EMF
θ: angle between field and velocity (motion)
 list factors of

Induced Electromotive Force induced EMF

Motion (velocity) is Motion (velocity) is Motion (velocity) is diagonal

parallel or antiparallel to perpendicular to magnetic to magnetic field
magnetic field field 0o < θ < 90o or
θ = 0o ⟹ EMFmin = 0 θ = 90o ⟹ EMFmax = vLB 90o < θ < 180o ⟹
θ = 180o ⟹ EMFmin = 0 EMF Between min and max

B 27 B B
P. 264
v
v v
B
v
 list factors of

Induced Electromotive Force induced EMF

Ex: A straight wire is part of a circuit that has a resistance of 0.50 Ω. The wire is 0.20 m
long and moves at a constant speed of 7.0 m/s perpendicular to a magnetic field of
strength 8.0 x 10–2 T.
𝑅=0 . 5
(a) What EMF is induced in the wire?
𝐿=0 .2
𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃 𝑣 =7
−2
¿ 7 (0 . 2)(8 ×10 )sin 90 𝐵=8 ×10
−2

¿ 0 .11V 𝜃=90
(b) What is the current through the wire? Electromotive force
𝐸𝑀𝐹 0 .11 Potential difference
𝐸𝑀𝐹 =𝐼𝑅 𝐼=
𝑅
=
0.5
=0 . 22 A Voltage
 list factors of

Induced Electromotive Force induced EMF

Ex: A straight wire is part of a circuit that has a resistance of 0.50 Ω. The wire is 0.20 m
long and moves at a constant speed of 7.0 m/s perpendicular to a magnetic field of
strength 8.0 x 10–2 T.
𝑅=0 . 78
(c) If a different metal were used for the
wire, increasing the circuit’s resistance to
𝐿=0 .2
0.78 Ω, what would the new current be? 𝑣 =7
−2
𝐸𝑀𝐹 =0 .11 𝑅 =0 . 78′ 𝐵=8 ×10
𝜃=90
𝐸𝑀𝐹 0 . 11
𝐼= = =0 . 14 A
𝑅
′
0 .78
 calculate

Induced Electromotive Force induced EMF

P. 107

38 87
P. 264 P. 268

𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃 𝐸𝑀𝐹 =𝐼𝑅

¿ 20 (0 . 5)(0 . 4)sin 90 𝐸𝑀𝐹
𝐼=
𝑅
¿ 4V
𝐸𝑀𝐹 4
𝐼= = =0 . 7 A
𝑅 6
 calculate

Induced Electromotive Force induced EMF

P. 107

37 48
P. 264 P. 265

𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃
−5
¿ 125 (25)(5 ×10 )sin 90
¿ 0 .16 V
 calculate

Induced Electromotive Force induced EMF

P. 107

36, 39 88
P. 264 P. 268

𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃 𝐸𝑀𝐹 =𝐼𝑅

𝐸𝑀𝐹 𝐸𝑀𝐹
𝐵= 𝐼=
𝑣𝐿sin 𝜃 𝑅
6 𝐸𝑀𝐹 6
𝐵= ¿
2 (30) sin 90
0 .1 T 𝐼=
𝑅
= =1 .2 A
5
 calculate

Induced Electromotive Force induced EMF

P. 265
B

𝐸𝑀𝐹
𝐿=
𝑣𝐵 sin 𝜃
 calculate

Induced Electromotive Force induced EMF

P. 267

76
P. 267

P. 266
∆ 𝑉 =𝐼𝑅 𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃
 calculate

Induced Electromotive Force induced EMF

J =N m
𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃 C= As
V =J /C
( )
[ 𝐸𝑀𝐹 ] = m
s ( ) ( )
( m ) (T )=
m
s
(m)
N
Am
=
Nm J
= =V
As C
 identify direction

Induced Electromotive Force of induced EMF

The direction (polarity) of electromotive force EMF (thus

conventional current) is determined by right hand rule.
𝐼 +¿
Thumb: first vector after equality sign (v)
Fingers: second vector after equality sign (B) −
Palm: quantity before equality sign (EMF)

The direction of induced current is same as the direction 𝐸𝑀𝐹=𝑣𝐿𝐵 sin 𝜃

of electromotive force.

One vector on x-axis: either right or left

One vector on y-axis: either upward or downward
One vector on z-axis: either into page or out of page out of page into page
 indicate direction

Induced Electromotive Force of induced EMF

EX:
into page
indicate the direction of EMF 38
P. 264
downward

out of page 63
P. 266

28 61
P. 264 zero P. 266
 indicate direction

Induced Electromotive Force of induced EMF

EX:
indicate the direction of EMF and induced current
 calculate induced EMF

Induced Electromotive Force and identify its direction

P. 249

P. 265
 explain microphone

Microphone principle

Microphone:
device converts sound waves into electric energy.
microphone is an application of electromagnetic induction.

A microphone consists of a thin aluminum diaphragm

attached to a coil in a magnetic field

Principle (how it works)

sound waves cause the diaphragm to vibrate. Then coil
moves in the magnetic field which induces an EMF (and
current) across the coil.

The induced EMF and current vary as the frequency of the sound varies.