Electricity in the Home

– Direct Current – D.C. is current that travels in one direction only, e.g. from a battery. On a Cathode Ray Oscilloscope, D.C. looks like:


Alternating Current – A.C. is current that constantly changes direction, e.g. from mains electricity (50Hz, 240V). On a CRO, A.C. looks like:

Two-way Switches –

The bulb can be switched on/off regardless of the position of the other switch.

The earth wire acts with the fuse to protect the user: If a fault occurs, a large current flows down the low resistance earth wire.

This melts the fuse on the live wire.

Thus, protecting the metal casing from becoming live and protecting the user from electrocution.  Some products have a plastic (insulator) casing to protect the user. This is known as double insulation. The circuit symbol for double insulation is: