1. Safety / Intro
The mains supply and batteries are sources of Electrical Energy
Electrical Appliances are Energy Changers

2. Power
Heat producing appliances have a power rating greater than 1000 Watts
Power Rating is the amount of energy used per second
Appliances greater than 700 W are protected by a 13 A fuse

3. Fuses
This protects the flex from overheating, melting and causing a fire.
Fuses are connected to the LIVE pin.
When the fuse blows it isolates the appliance from the ‘high voltage’ supply

4. Plugs
Mains Plugs

5. Human Conductivity We conduct electricity very well
When wet the body’s conductivity increases
Bathroom light switches, shower switches are either outside the bathroom or on a cord

6. Earth Wire Connected to casing of metal appliances
If live wire touches the casing ‘ current flows through earth wire to ground ( often via the water pipes )
A large current flows , blowing the fuse and isolating the appliance from the high voltage mains.

7. Double Insulation
Appliances with casings made of plastic DO NOT need an earth wire
The casing is an insulator

8. Electric Current Q = I x t This is a Flow of Charged Particles
Charge Current Time
Coulombs ( C ) Amps ( A ) Seconds ( s )

9. Voltage Energy Given to each coulomb of charge Units are Volts ( V )
Measured by Voltmeter ,
Connected in parallel

10. Current This is a flow of Charged Particles Units are Amps, ( A )
Measured using an Ammeter
Connected in Series

11. Series Circuits Current is the SAME at ALL points
Voltage across Supply equals the voltage across Resistor 1 + voltage across resistor 2
Vs = V1 + V2

12. Parallel Circuits Voltage across each branch is the same
Current through resistor 1 plus current through resistor 2 equals the supply current
It = I1 + I2

13. Resistance Ohm’s Law V = I x R at constant Temp
Resistance : measure of how easy it is for charges to flow.
V = I x R
Volts ( V ) Amps ( A ) Ohms (

14. Series Resistors

15. Parallel Resistors

16. Variable Resistors A length of wire is wrapped into a cylinder
Different lengths can be tapped into
The longer the length the bigger the resistance
The bigger the resistance the lower the current

17. Variable Resistors Uses Light Dimmer Switches Volume controls
Speed Controls
Temperature Controls for grills/ ovens …
Computer Joysticks
Fuel gauges

18. Continuity Tester
Used to detect ‘Open Circuits’ or Breaks in Circuits such as blown bulbs.
Component is blown if there is NO reading on the meter.

19. Power
This is the amount of energy transferred per second. Units are Watts ( W ).
Heat producing appliances have big power ratings

20. Power
Power can also be calculated from

21. Lamps Discharge Lamps ( Fluorescent Tubes )
An electric current passes through the gas
Virtually NO heat Energy is produced
MUCH more efficient than
Filament lamps
An electric current is passed through a piece of resistance wire which heats up
Produces more heat energy than light energy

22. Direct Current Current flows in one direction ONLY
Electrons flow from Negative to Positive
Size of Voltage remains constant
Batteries supply D.C.

23. Alternating Current Mains electricity is A.C.
The current constantly changes direction
Mains electricity is 50 Hz , 50 cycles in 1 second
The size of the voltage is constantly changing. Quoted value ( 230 V mains )is smaller than the peak value
Peak value, 325 V for mains
Quoted value, 230 V
Current flows when below 0V line
0V Line

24. Behind the Wall
Household appliances are connected in parallel : same voltage ( 230 V ) and independent switching
Sockets are wired in a RING circuit:
Current flows via 2 paths therefore smaller currents flow and thinner cable can be used
Less cable needed than conventional parallel
Easy to add extra sockets

25. Behind the Wall
Lighting circuit draws less current than Ring circuit for sockets
Lighting circuit conventional parallel
Lighting circuit uses a 10A circuit breaker as opposed to a 30A on the ring circuit

26. Fuses / Circuit Breakers
Mains fuses protect the mains wiring
Circuit Breaker is an automatic switch that switches off when current exceeds stated value
Circuit breakers can easily be reset and used again but fuses must be replaced

27. Kilowatt Hours I unit of electricity is 1kWh
I.e. A 1kW appliance switched on for 1 hour
total units = Power (kW) x time ( hours )
1 kWh = Power x time
1000 W x 60 x 60 seconds
= Joules

28. Electromagnetism a
When a current flows there is a Magnetic Field around a wire
If a wire is placed inside a magnetic field it experiences a force N S S N
Current flows out of board
Current flows into board S N

29. Electromagnetism Relays Motors Bells Loudspeakers Tape Recorders
All use Electromagnetic effect

30. The d.c. motor d 8 Rotation is produced N S
Each side of the coil experiences forces acting in opposite directions the coil rotates a
Rotation is
produced N S
+VE
-VE

31. d.c. motor 9 a
If the flow of current WAS NOT reversed then the coil would flip back
A SPLIT RING COMMUTATOR reverses the flow of current a N
+VE
-VE S

32. a
The d.c. motor b
The coil continues to rotate N S
+VE
-VE

33. Commercial motors More coils : more powerful motor, smoother turning
Electromagnets instead of permanent magnets : increased magnetic field, switched on / off
Brushes as contacts : mould themselves to shape of commutator

34. Commercial motors