P4

Electrostatic dust precipitators remove smoke particles from chimneys before they are carried out by the hot air and cause pollution. The precipitators make use ofelectrostatic charge to attract the smoke particles or dust.

1- metal plates or grids are put in the chimneys.

2- They are charged by connecting them to a high potential difference (pd) or voltage.

3- The dust particles are attracted to the charged plates or grids.

4- They clump together on the plates to form larger particles.

5- When they are heavy enough, the dust particles fall back down the chimney into containers.

A fuse is a thin piece of wire. It is a weak link in the circuit.

If the current gets too large, the fuse:

- will melt.

- break the circuit and prevents the flow of the current.

This prevents the flex of overheating and causing a fire which prevents further damage to the appliance.

Fuses will not stop you getting an electric shock they take too long to melt. After it has melted the fuse must be replaced.

- A 2 amp fuse melts when a current of 2 amps flows through it.

- A 13 amp fuse melts when 13 amps flows through it.

You should fit the lowest fuse that will carry the normal operating current.

Circuit breakers are switches that switch the current off when it gets too high. They can be switched on again once the fault is corrected .

A residual current device (RCD) is a circuit breaker that switches off very quickly. It will protect you from receiving an electric shock.

A tracer can be used to detect a leak or a blockage in a pipe.

- The tracer is added to the fluid in the pipe.

- A gamma source is used so it can penetrate to the surface.

Alpha sources are used in Smoke detectors.

- Alpha particles from the source ionise atoms in the air (into electrons and positive ions) so that the air can conduct electricity.

- A small current flows and a sensor detects it.

- If smoke blocks the path of the positive ions and electrons, there is no current and the alarm sounds.

Radioactive dating.

Rocks contain radioactive isotopes of uranium. The older the rock, the more of the isotope will have decayed to an isotope of lead. We can use the ratio or uranium to lead to date the rock.