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. A generator converts mechanical energy into electrical energy
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

9. Generators and AC

10. Generators and AC

11. 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

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

13. 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

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

15. This device is known as a transformer
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

16. Used to step voltages up or down
Transformers
Used to step voltages up or down
i.e. Used in AC adaptors

17. 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

18. 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

19. 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

20. Electromagnetic Waves

21. 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

22. 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