Electromagnetic induction builds on the concept of magnets and magnetic fields in grade 10. Most of the work covered here is quite clear and straight forward.

1. Electromagnetic
Induction

2. Electromagnetic Induction
• When a magnet and a wire move
relative to each other, a voltage is
induced
• Amount of voltage produced depends
on:
–Speed: High speeds produce high voltages
–Magnetism: Strong magnets produce high
voltages
–Shape of Wire: Many coils in the wire
produce high voltages

3. Electromagnetic Induction

4. Electromagnetic Induction
Note: It is more difficult to push the magnet into a coil
with more loops because the high current generates a
stronger magnetic field which acts against the magnet.

5. Electromagnetic Induction
• Electromagnetic Induction: Inducing
voltage by changing the magnetic field
around a conductor
–ANY change in magnetic field will induce a
voltage
–i.e.) Traffic control signals

6. Faraday’s Law
The induced voltage in a coil is
proportional to the number of loops
multiplied by the magnetic field
changes within those loops.

7. Faraday’s Law
• When a magnet moves past different
materials, the voltage induced is the same
for each case
• The most current will be produced in the
material where the electrons are bound
most loosely
–i.e.) The magnet will produce a larger
current when moving past copper than
rubber

8. Bell Ringer
• To produce a current in a coil of wire with a
magnet, what must occur?
• What type of current will this produce?

9. Generators and AC
• As a wire moves back and forth past a
magnet, the resulting current changes
direction (AC)
• Recall: A motor converts electrical
energy (from the battery) into
mechanical energy (rotation of the
armature)
• A generator converts mechanical
energy into electrical energy

10. Generators and AC

11. Generators and AC

12. Generators and AC
Turbine: When the armature of a generator is
connected to a wheel which captures wind, water, or
steam in order to turn and produce electrical energy

13. Bell Ringer
• Explain what the difference is between a
generator and a motor in terms of energy.

14. Transformers
• Consider two coils
side by side:
–Primary Coil:
Connected to a
voltage source
–Secondary Coil:
Connected to a
galvanometer

15. Transformers
• When the voltage source is turned on:
–Current briefly surges through the secondary
coil
• When the voltage source is turned off:
–Current briefly surges through the secondary
coil in the opposite direction
• The magnetic field building around the
primary extends to the secondary
–Changes in magnetic field intensity induce
voltage in the secondary

16. Transformers
• Placing a core within the coils will
intensify the magnetic field
• The secondary will intercept more of
the field change

17. Transformers
• Instead of switching a DC voltage
source off and on, the device is
connected to an AC voltage source
• The rate at which the magnetic field
changes = frequency of the AC
current
• This device is known as a transformer

18. Transformers
• Used to step voltages up or down
–i.e. Used in AC adaptors

19. Transformers
• Voltage is stepped up:
–When the number of coils (turns) in the
secondary > number of turns in primary
• Voltage is stepped down:
–When the number of coils (turns) in the
secondary < number of turns in primary
• Since voltages can be stepped up and
down so easily, electrical power is
primarily in the form of AC

20. Induction of Electric and
Magnetic Fields
• According to Faraday:
–Electric fields are created in any region of
space where a magnetic field is changing
with time.
• According to Maxwell:
–A magnetic field is created in any region of
space where an electric field is changing
with time.
• These laws are inverses of each other and
lead to the concept of electromagnetic waves

21. Electromagnetic Waves
• Composed of vibrating electric and
magnetic fields the regenerate each
other
–Waves move outward from a vibrating
charge
–E.F. is always perpendicular to the
M.F. and both are perpendicular to the
direction of the moving wave

22. Electromagnetic Waves

23. Electromagnetic Waves
• All electromagnetic waves move at
the speed of light
–Discovered by Maxwell
• Changing electric fields constantly
induce changing magnetic fields and
vice versa
–If the waves traveled at less than the
speed of light, they would rapidly die
out

24. Electromagnetic Waves
•Maxwell found that light is simply
an electromagnetic wave vibrating at
a specific frequency
•4.3x1014
to 7x1014
vibrations per second
•This frequency stimulates the retinas
in our eyes and allows us to see these
waves