1. Electromagnetic Induction
Lenz’s Law
Faraday’s Law
Can be very conceptual…

2. Generators…. How do we make Electricity…

4. What is Electricity? Electricity is energy transported by
the motion of electrons
**We do not make electricity, we CONVERT other energy sources into electrical energy**
Conversion is the objective…

5. Electric Motor M
Electrical
Energy
Mechanical
Energy
DC Motor

6. Electrical Motors transform electrical energy into mechanical energy.
Electric Generators do the opposite. They transform mechanical energy into electrical energy.
The process of using a changing magnetic field to create electric current is called electromagnetic induction.

7. Electric Generator G
Mechanical
Energy
Electrical
Energy

9. How is V and I induced?

10. If a conducting bar is moved along conducting rails as shown below, there will be a voltage (ε) and current (I) induced in the direction indicated:

11. Faraday’s Law is used to determine the induced Voltage
Faraday’s Law is used to determine the induced Voltage. Two algebraic forms of Faradays law:
The current direction is given by Lenz’s law…
ngsir.netfirms.com/englishhtm/Induction.htm
The induced Voltage (ε) can be increased by
Using a stronger magnet (B)
More turns on the coil (L)
Moving the magnet faster (v)

12. “L” ~ wire length that cuts the
magnetic field lines

14. E A magnetic field can be used to separate + and – charges. - +
If a conducting rod moves through the field, then the + and – ions will drift to opposite ends of the rod and form an electric field across the rod.
● ● ● ● ● ●
If the rod is draped across two wires and forms a closed loop, then current can develop in the loop… this is called induction. - E +
wires

15. Electromagnet N S
Which way would the current need to be flowing in order to make this electromagnet repel this permanent magnet?
A. top wire
 bottom wire
 top wire
 bottom wire
C. Can’t be determined
D. Don’t know

17. Why is their Induced Current and what of its direction?

18. Lenz law When the N pole is moved into the coil a current flows.
The direction of the current is such that it produces a field that opposes the change causing it.
The end of the coil nearest the magnet becomes N (direction from solenoid rule). N S S N N S A
Work is done against this opposing magnetic field to produce electricity.
If this did not happen the law of conservation of energy would be broken (free energy!).
The induced current always flows in the direction that opposes the change causing it.
This effect is know as Lenz law.

19. Loop is pushed into the uniform B field.
Force in wire BC due to Lenz’s law
Current direction anti clockwise due to right hand slap rule
Loop is completely in the uniform B field ~ no induced current. Why ?
Induced current in wires AD & BC cancel each other out – no circuit
SKIP!
As the loop is leaving the uniform B field ~ induced current. Why ?
Force in wire AD due to Lenz’s law
Current direction clockwise due to right hand slap rule