Practise defining and calculating current, tracing conventional current and electron flow, connecting ammeters and distinguishing alternating from direct current traces.
The charge on the sphere in (b) is . A high resistance wire is now connected between the sphere and earth. It takes 20 minutes for the sphere to become completely discharged through the wire.
Suggest why there is a current in the wire between the sphere and earth.
Calculate the average current in the wire between the sphere and earth.
A lightning conductor protects a tall building and the people in it against damage and injury caused by lightning strikes.
The lightning conductor is a very long strip of copper that is attached to the side of the building. At the top of the building, the strip of copper is connected to a vertical metal pole and at the bottom of the building, it is buried in the ground.
Fig. 7.1
The bottom of the thundercloud is negatively charged.
As the cloud moves closer to the building, the top of the metal pole becomes charged.
As the cloud passes over the building, a lightning strike occurs and a charge of 0.84 C flows through the lightning conductor. The charge flows for .
Calculate the average current in the lightning conductor during this time.
It is suggested that the current in the lightning conductor could be measured by connecting a laboratory ammeter between the pole and the copper strip.
State one reason why this cannot be successful.
State, in terms of their structure, why metals are good conductors of electricity.