1. Generating Electricity
To generate a voltage (electricity) you need:
a magnetic field
a conductor
movement V
The size of the voltage induced depends on:
strength of the magnets (magnetic field)
the length of coiled wire (conductor)
speed of movement

3. The Dynamo
coil
As the dynamo is turned, the magnet rotates beside the coil of wire.
An A.C voltage is generated in the coils
Power station generators are much bigger and use electromagnets.
electrical output
rotating magnet

4. (rotating electromagnets)
STATOR
(stationary coils of wire)
ROTOR
(rotating electromagnets)
Generator turbine shaft
Turbine Blades

9. M.A.R.S Floating Wind Powered Generator

10. Info
Speaking of R2-D2, this M.A.R.S. Floating Wind Generator looks a lot like a flying R2 droid on its side. This helium-filled, horizontal-rotating M.A.R.S. (Magenn Power Air Rotor System) will go into production with its 4.0 kw unit this year with 7 more models planned for release in the next 4 years. The 2010 and 2011 planned models will be able to power a small town on their own.
The generated electrical energy travels town its 1000-foot tether rope, with the energy available for immediate use. With its helium, balloon-like flying system, M.A.R.S. can fly higher than other wind turbines, able to reach altitudes with much higher wind speeds.

11. Size of Voltage
Experiment
dynamo
oscilloscope

12. greater amplitude (bigger voltage) higher frequency (faster rotation)
Results
slow speed
high speed
greater amplitude (bigger voltage)
higher frequency (faster rotation)

13. transformers require an AC voltage
A transformer consists of 2 coils of wire and iron core which passes through both coils.
iron core
primary coil
secondary coil
transformers require an AC voltage

14. secondary voltage (VS)
The circuit symbol for a transformer is:
An AC voltage in the primary coil induces (creates) a voltage in the secondary coil.
The size of the secondary voltage depends on:
size of primary voltage
number of turns on each coil. NP VP VS NS
Quantity
Unit
secondary voltage (VS)
primary voltage (VP)
secondary turns (NS)
primary turns (NP)
volts (V)
** NO UNIT **

15. This is a STEP DOWN transformer
Example 1
Calculate the secondary voltage for the transformer shown.
1000 T
230 V AC VS
52 T
This is a STEP DOWN transformer

16. This is a STEP UP transformer
Example 2
Calculate the secondary voltage for the transformer shown.
300 T
50 V AC VS
12,000 T
This is a STEP UP transformer

17. Current in TransformersNP IP NS IS

18. Calculate the current in the secondary coil.
Example 1
Calculate the current in the secondary coil.
0.1 A IS
1000 T
50 T

19. Calculate the voltage and the current in the secondary coil.
Example 2
Calculate the voltage and the current in the secondary coil.
0.05 A IS
230 V VS
10,000 T
500 T
Voltage

20. Current

21. Transformer Power & Efficiency
If the transformer is 100% efficient:
To calculate power we use
So this gives us the formula
** NOT on data sheet **

22. Example 1
Calculate the current in the secondary coil, assuming the transformer is 100% efficient.
0.04 A IS
50 V
12 V

23. Example 2
Calculate the current in the secondary coil, assuming the transformer is 90% efficient.
0.08 A IS
230 V
12 V
Power in Primary
Power in Primary

24. Power in Secondary
Current in Secondary

25. step-down transformer
Power Lines
Electricity is provided by power lines called The National Grid.
400,000 V
230 V
25,000 V
step-up transformer
step-down transformer
The output voltage is stepped up to reduce power loss in the wires of the national grid.

26. Stepping up the voltage reduces the size of the current.
Smaller current, less power loss.
Example 1
A transmission power line of length 60km has a resistance of 2 Ω per kilometre. The total current in the cable is 50 A.
Calculate the power loss in the transmission line.