Section 2 b) Specification

2.2 understand and identify the hazards of electricity including frayed cables, long cables, damaged plugs, water around sockets, and pushing metal objects into sockets

2.3 understand the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances

2.4 understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature, and how this can be used in a variety of domestic contexts

When there is an electrical current flowing through a wire, there is energy transfer which causes a heating effect. Higher currents cause more heat to be emitted, which means there is more resistance, causing less current to flow at the same voltage.
This effect can be used to our advantage, the principle is used in fuses: they melt when too much current is flowing because they heat up.
It can also be used in other appliances. Toasters and kettles often contain high resistance wires that heat up and boil our water or cook our toast. This was also used in old-style light bulbs, but since then more efficient ways have been developed.

2.5 know and use the relationship:
power = current × voltage
P = I × V
and apply the relationship to the selection of appropriate fuses

If an appliance has a power rating of 1000 W and 230 V, we can use this relationship to determine that the current is 1000 / 230, which equals 4.3 A. So in selecting a fuse, we would choose one that is close, but just slightly higher to normal operating current. In this case, a 5A fuse would be selected.

2.6 use the relationship between energy transferred, current, voltage and time:
energy transferred = current × voltage × time
E = I × V × t

If we know the current in an appliance is 2A and it is connected to a 4.5V battery, what is the energy transferred over 5 minutes?
2 x 4.5 x 5 x 60 = 2700 joules

2.7 understand the difference between mains electricity being alternating current (a.c.) and direct current (d.c.) being supplied by a cell or battery.

Alternating current means the current is constantly changing direction. Mains electricity is alternating current because it is easy to transport long distances, and easily converted using a transformer (advantageous because it allows current to be reduced and therefore less resistance will happen in power lines and therefore less energy lost)

^a.c. reading on an oscilloscope

Direct current means the direction of current does not change. This means it will provide a constant voltage.

^d.c. reading on an oscilloscope