1. Menu
Generating electricity
Transformers
AC & DC

2. AC & DC

3. Alternating Current (AC)
Voltage
The current changes direction 50 times every second (frequency = 50Hz)
Time
AC is easier to generate than DC

4. If the cell is reversed the current flows in the opposite direction
Direct Current (DC)
The current only flows in one direction
Voltage
Time
If the cell is reversed the current flows in the opposite direction
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5. Generating Electricity

6. Generating Electricity
We can generate electricity through Electromagnetic Induction………
Electromagnetic Induction: The Creation of a Voltage (and maybe a Current) in a wire which is experiencing a Change in Magnetic Field

7. Electromagnetic Induction
The ‘field lines’ have to be cut. No current is produced if the magnet is not moving! N
If You push a magnet into a coil the electrons in the coil are also given a push. This makes an ‘induced voltage’

8. Electromagnetic Induction
Notice the needle moves in the opposite direction N
If You pull a magnet out of the coil the electrons in the coil are once again given a push. This makes an ‘induced voltage’ in the opposite direction

9. How Can You Increase the Size of the Induced Current?
Move the Magnet Faster
Use a Stronger (not bigger!) Magnet
Put more Turns on the Coil

10. Will it make AC or DC Current?
We can use a magnet, coil and movement to generate electricity with this device
Will it make AC or DC Current?

11. This is a Generator
You will have heard them near road works generating the electricity to make the traffic lights and machines work

12. AC Generator Induced current can be increased in 4 ways:
Increasing the speed of movement
Increasing the magnetic field strength
Increasing the number of turns on the coil
Increasing the area of the coil

13. Bikes often have Dynamos to make electricity to light a bulb
Dynamos are slightly different from generators as they rotate the magnet

14. If the Needle on the Centre Spot Galvanometer Moves Right 1 Division When the Magnet Is Placed Into the Coil, What Happens When….
The magnet is pulled out at equal speed?
The magnet is put in faster?
The magnet is left motionless inside the coil?

15. 1) Explain what happens when the handle turns at a constant rate
Use the Key Words in your answer:
Magnet, coil, flux, a.c, bulb shines, movement
2) Give 3 methods to increase the brightness of the bulb
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16. Transformers

17. Transformers Transformers transform (change) the Voltage
Transformers only work on AC because there is constantly changing flux

18. Step Up & Step Down Primary Coil Secondary Coil Primary Coil
Step Up Transformer
More turns on the Secondary Coil
Step Down Transformer
More turns on the Primary Coil

19. Some Transformers Look Like This…..
…..you might have heard their characteristic ‘hum’

20. The Transformer Equation
Primary voltage = Number of turns on Primary
Secondary voltage Number of turns on Secondary
The ratio of the turns on the coils equals the ratio of their voltages

21. No. of Turns on Secondary
Complete the table
Primary Voltage
Secondary Voltage
No. of Turns on Primary
No. of Turns on Secondary
Step Up or Step Down?
12V
36V
100 ?
600V
300V 20
20,000V
50,000V
1,000
23V
230V
150
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