Download Chapter 37 Electromagnetic Induction

Warm-up
• Why do loops of wire in a motor rotate?
• What is similar between Electric motor,
and Electric meter?
• What is electromagnetic induction?
• Name 4 objects that apply
electromagnetic induction.
Chapter 37:
Electromagnetic Induction
•
1.
Faraday discovered:
Magnetic and
Electric fields
interact to produce a
Force.
(3rd right hand rule)
2. Magnetism can
produce electric
current in a wire!!
• How so?
• Michael Faraday
Electromagnetic Induction
• The phenomenon of inducing voltage
in a conductor by changing the
magnetic field near a conductor is
known as Electromagnetic Induction
Magnetic field changes
when either the magnet
or the coil moves or
when they both move.
Faradays experiment
• Molecular Expressions: Electricity
and Magnetism - Interactive Java
Tutorials: Faraday's Magnetic Field
Induction Experiment
Induced Voltage?
• why is the phrase Induced voltage used
instead of induced current?
• Answer:
– In order for current to flow between two
points of a conductor, there must be a
difference of potential between those points.
That potential difference is the voltage.
Therefore, Voltage is induced first in order
for current to flow.
Electromagnetic induction
• video
• http://glencoe.com/sec/science/phys
ics/ppp_09/animation/Chapter%202
5/Electromagnetic%20Induction.swf
Magnitude of the induced voltage
•
•
What factors affect the magnitude
of the induced voltage?
Answer:
1. The rate (R) at which Flux (magnetic
field) is changing,
2. The number of coils/turns (N) of the
conductor
The Faradays law.
• Induced voltage (V) in a coil is
proportional to the product of;
– the rate (r) at which the magnetic field
changes within the loops, and
– Number (n) of loops (turns /coils)
v ~ r n
Question;
• Why is it
hard to
move the
magnet into
the coil if
the coil has
many loops?
Lenz’s Law
• The law notes that;
– an induced voltage always produces a
magnetic field that opposes the field
that originally produced it.
Lenz’s law
Application of electromagnetism
• Generator
• The coil is rotated
mechanically using
one’s hand,
• Other ways of rotating
the coil include
– Water-hydro power
– Wind- wind mills
– Steam• Geothermal,
• Nuclear Reactors
application
• Name 4 objects
that apply
electromagnetic
induction.
•
•
•
•
Transformer
Generator
Motor
Electro magnet
Homework
• Textbook pg 592 # 1-10
The transformers
A simple transformer
• A simple transformer is a set of
induction coils as shown below.
Primary coil induces voltage
onto the secondary coil
Primary and secondary
coils
• A common transformer
is made up of an iron
core and two coils of
wires as shown below.
• The Primary coil is
connected to the power
source.
• The secondary coil
gets induced with
current.
What does it do?
• Molecular Expressions: Electricity and
Magnetism - Interactive Java Tutorials:
Transformer
Induction process (Mutual induction)
• Happens when current in the primary is changing
(increasing or decreasing).
• Changing current induces a magnetic field that is
changing continuously on the core, a condition
necessary for induction of voltage continuously on to
the secondary coil.
• When current is not changing (increasing or
decreasing), there is no induction taking place.
Why is the AC preferred to DC?
• We can increase and decrease current flow
by opening and closing (Switching off and on)
the circuit continuously when using a DC
current, or just use AC current. The Ac is
changing continuously
Why is an Iron core preferred
to two coils apart?
• Answer:
Iron core concentrates the magnetic
field within itself by forming loops that
get into contact with the secondary coil.
These loops of magnetic field induce
voltage in the secondary coil.
Step up Transformers
• The number of coils
in the secondary and
primary determines
whether a
transformer is a
step up or step
down transformer.
less number
of coils in
primary
more number
of coils in
secondary
Step down Transformers
Notice that power transferred is the
same.
More number
of turns in
primary coil
Less
number of
turns in
secondary
• What is the relationship between primary
voltage, secondary voltage and the number
of turns?
• Answer:
Vp
Vs

Np
Ns
•
The relationship between in-put
and out-put power is:
Power input = power output.
I p  V p = Is  Vs
Class work & Homework
• Textbook Page 592, # 11-15
• Hm WK Textbook page 594, # 34-42