Explain why the student should open the switch after each reading.
resistor would get hot if current left on
so its resistance would increase
Why does the hairdryer not need an earth wire?
case is plastic
What is meant by specific latent heat of fusion?
amount of energy required to change the substance from solid to a liquid and has a unit mass
Describe the action and purpose of a solar panel.
water heated by radiation
water used to heat buildings
A fuse is connected in the live wire.
RCCBs are sometimes preferred to fuses because they react faster
The two wires are the live and neutral wires.
What do the letters a.c. stand for?
alternating current
Describe the advantages and disadvantages of keeping the road clear of ice using
energy storage
salt
undersoil electrical heating
energy storage advantages
no fuel costs
no environmental effects
disadvantages
-expensive to set up and maintain
-need to dig deep under road
salt spreading advantages
easily available
cheap
Salt spreading disadvantages
can damage trees
needs to be cleaned away
undersoil heating advantages
not dependent on weather
can be switched on and off
undersoil heating disadvantages:
costly
bad for environment
mains electricty is what type of supply
AC supply
UK Frequency of AC
50Hz (hertz)
UK voltage of AC
230V
What is alternating current
It comes from the mains. The current continuously varies, from positive to negative(charges changes direction)
What is direct current?
The movement of charge in one direction only- cells and batteries provide this
How many wires in a plug
3 wires
Live wire colour
Brown
Live wire voltage
230V
Purpose of live wire
carries alternating p.d from the supply
Why is the live wire dangerous?
our bodies are at 0 V. If you were to touch a live wire, a big potential difference will act across your body, causing a current to flow through you. this causes a large electric shock which could injure or even kill you. And even if the mains circuit is off, current may still be flowing through it
Neutral wire colour
Blue
Neutral wire voltage
0V
Neutral wire purpose
Completes the circuit
Earth wire colour
Green and yellow stripes
Earth wire voltage
0V
Purpose of earth wire
It only carries a current if there is a fault, it is a safety wire to stop the appliance becoming live
Electrical energy transfer examples
Kinetic energy for a motor and thermal energy in a kettle
Work done is equal to
Energy trasnferred
Greater power rating means....
More energy used
What is the national grid
A system of cables and transformers linking [power stations to consumers across the UK
What is transferred from power stations to consumers using the national grid
Electrical power
What do transformers to
Change the potential difference
What do step up transformers do
Increase the pd from the power station to the national grid
Why do step up transformers increase the pid
As the power is constant, current decreases so less energy is lost
What do step down transformers do
Decrease the pd from the national grid to consumers