2b.1 - Electricity in the Home Flashcards
What voltage is the UK mains supply?
230 V
What type of supply is the mains?
AC supply
What does AC stand for?
Alternating current
What is an alternating current?
The current is constantly changing direction - from positive to negative and back
What is the frequency of the AC mains supply?
50Hz
What is the unit for frequency?
Hz
What does Hz mean?
Cycles per second
What type of supply is for batteries?
DC
What does DC stand for?
Direct current
What is a direct current?
The current always flows in the same direction
What does the vertical height on an AC trace show you?
The input voltage - potential difference
How do you calculate the voltage for a DC current on an oscilloscope?
The distance from the straight line to the centre line
How do you calculate frequency?
1 % time period
Name the nine examples of electrical hazards in the home
- Long cables
- Frayed cables
- Cables in contact with something hot or wet
- Water near sockets
- Shoving things into sockets
- Damaged plugs
- Too many plugs in one socket
- Lighting sockets without bulbs
- Appliances without covers
What colour is the earth wire?
Yellow and green striped
What colour is the neutral wire?
Blue
What colour is the live wire?
Brown
What is the live wire? (3)
- Brown
- Alternated current - High
- Current flows in
What is the neutral wire? (3)
- Blue
- Stays at 0V
- Current flows out
What is the earth wire? (3)
- Green and yellow striped
- For safety
- Attached to the metal casing and carries electricity to the earth
What wire is screwed to the pin at the top of the plug?
Earth
What wire is screwed to the pin at the left of the plug?
Neutral
What wires screwed to the pin at the right of the plug?
Live
What are the safety features of a plug? (4)
- Right wire in right pin
- No bare wires
- Cable grip
- Thick cables
What are the features of a plug? (2)
- Metal parts made from copper or brass because they are good conductors
- The case, cable grip, and cable insulation are made of rubber or plastic because good insulators and flexible
What prevents electrical overloads?
Earthing and fuses
How does the earth wire protect the appliance? (3)
- If live wire touches casing
- Too great a current flows in through the live wire
- Current flows through the case and down the earth wire
How does the fuse protect the appliance? (3)
- Surge in current melts fuse or trips the circuit breaker
- This cuts off the live supply and breaks the circuit
- This isolates the appliance
How should fuses be rated?
Just higher than the normal operating current
What is a double insulated appliance? (2)
- An appliance that has a plastic case and no metal parts showing
- Doesn’t need an earth wire
What are the advantage circuit breakers have over fuses?
- A circuit breaker’s switch can be closed but you have to buy a new fuse
- Faster as doesn’t need to wait for fuse to melt
- Safer as detects smaller currents
What is an disadvantage of circuit breakers over fuses?
Much more expensive
Name a type of circuit breaker
RCCB’s
What does RCCB stand for?
Residual Current Circuit Breaker
How does and RCCB work?
Detects the difference in current between the live and neural wire and cuts of power quickly by opening a switch
What do all resistors produce when a current flows through them?
Heat
What is meant of an efficient appliance?
It wastes less energy
A 2.5 kW kettle is on for 5 minutes. Calculate the energy transferred by the kettle in this time.
Energy transferred = Power rating x time
2500 x 300 = 750 000 kJ = 750 kJ
A hair dryer is rated at 230 V, 1 kW. Find the fuse needed.
Power = Current x Potential difference
1000 % 230 = 4.3 A. The fuse should be higher than normal so a 5 AMP FUSE is used.
The motor in an electrical toothbrush is attached to a 3 V battery. If a current of 0.8 A flows through the motor for 3 minutes:
a) Calculate the total charge passed
b) Calculate the energy transformed by the motor
Energy transformed = Charge x Potential difference
a) 0.8 x (3 x 60) = 144 C
b) 144 x 3 = 432 J
