1. Applications of Electromagnetism

2. Electromagnetic Waves

3. A changing magnetic field generates an electric field.
B  E
A changing electric field generates a magnetic field.
E  B

4. changing E changing B changing B changing E ELECTROMAGNETIC WAVE
speed = c (speed of light; 3.00 x 108 m/s)

5. EM Wave

6. v
E ┴ B ┴ v

7. To produce an EM wave:
EM waves produced by accelerated
electric charges.

8. Electromagnetic Spectrum
v = λ f

9. Transformers

10. A changing magnetic field in the primary coil induces a current in the secondary coil.

11. Use an alternating current to produce a constantly
changing magnetic field.

13. EMF in a coil depends on the number of turns of wire in that coil.
Step-up Transformer
EMF in a coil depends on the number of turns of wire in that coil.
EMF α N

14. Step-Down Transformer
Secondary coil has fewer turns (N) than the primary.
EMFs Ns =
EMFp Np

15. If there are no losses (ideal transformer),
Power in a Transformer
If there are no losses (ideal transformer),
Powerprimary = Powersecondary
Power = voltage x current
since voltage = EMF
EMFp x Ip = EMFs x Is

16. EMF α 1/I
Step-up transformer:
increases EMF, decreases current
Step-down transformer:
decreases EMF, increases current

17. Electric Power Transmission
Power loss in wires occurs when current is high.
Use step-up transformer to transmit power at high emf and low current (minimize power loss).

18. Electric Motor

19. Motor: Converts electrical energy into mechanical energy.

21. Commutators – switch the current direction in the armature coil every
wire wrappings
which turn
field poles
Commutators – switch the current
direction in the armature coil every
half turn

22. In an A.C. motor, input electricity continually switches direction; commutators not needed.

27. Maximum induced current when
cutting through lines of magnetism

28. Induced Alternating Current
With each ½ turn, wire in the
armature changes its direction of
motion in magnetic field.

29. A.C. Generator

30. D.C. Generator
To produce an output of D.C., use
commutators to switch current
direction.

31. Motor: converts electrical energy to mechanical energy
Motor vs. Generator
Motor: converts electrical energy to mechanical energy
Generator: converts mechanical
energy to electrical energy

32. When a motor is spinning, it also acts as a generator and generates an EMF opposite
the supplied EMF.
This is called the back EMF.