P5- Electricity in the home Flashcards
Direct current
Direction?
Magnitude?
From where?
Flows in one direction
Constant magnitude (doesn’t change)
From cells/batteries
Alternating current
Direction?
Magnitude?
From where?
Direction changes
Changes magnitude
From the mains supply
Order of the national grid
Power station—> step up transformer—> transmission cables—> step down transformer—> consumer
Step up transformer
Pd?
Current?
Key fact?
-Increases pd
-Decreases current
-Reduces energy to surroundings, more efficient
Step down transformer
Pd?
Current?
Key fact?
-Reduces pd
-Increases current
-Making it safe to use
The mains supply
Pd?
Frequency?
230V
50Hz
Equation to find frequency of an ac supply
-Measure time period of waves
Frequency= 1/ time taken for 1 cycle
Neutral wire
Where?
Colour?
Job?
Bottom left
Blue
Potential difference of 0v to complete circuit
Earth wire
Where?
Colour?
Job?
Middle
Green and yellow stripe
Low resistance, path for current to flow to the Earth if there is a fault
Live wire
Where?
Colour?
Job?
Bottom right
Brown
Provides potential dif of 230v
What does a metal cased appliance have and why?
Earth wire, if live wire touched the metal case and someone touched it they would be electrocuted
What does a plastic cased appliance have and why?
Double insulation, no Earth wire
Insulators don’t transfer electrical energy
What are the outer casing of plugs, sockets and cables made of and why?
Hard wearing insulators like plastic
What are the pins on a plug made out of and why?
Brass pins, good conductor, doesn’t rust or oxidise
What is a fuse and why do plugs have it?
A tiny piece of wire that heats up and melts if the current through it is too high. This breaks the circuit.
What are wires made out of and why?
Copper, good electrical conductor and ductile
Why are people electric shocked when touching a live wire?
The pd in the live wire is 230V and in a body it is 0V. This difference causes a large current to flow through them, which is dangerous
3 fuses for domestic appliances
Which type to choose?
3A, 5A, 13A
Fuse should be a slightly larger current than the device needs
Equation for the rating of a fuse?
Electrical power (W) / pd (V)
What happens to a resistor when charge flows through it?
Energy is transferred to the resistor so it becomes hotter
Why is efficiency always less than 100%
The device can’t make energy
What is a domestic electricity meter?
A device that measures how much energy is supplied
