This question was not popular among the candidates as it was attempted by few candidates. Performance was as follows
Part (a)(i): Candidates were able to describe lightning conductor correctly.
(ii) Candidates were not able to answer this question correctly due to poor
knowledge of principle of action of lightning conductors.
Part(b): Performance in this part was fair. However, few candidates indicated the arrows on the lines force wrongly.
- Correctly drawn and performance was fair
- Correctly drawn and performance was fair
- Poorly drawn. They did not mind the positive and negative charges performance was poor.
Part(c) Most candidates could not calculate this because they did not find their forces differently before calculating the distance required performance was poor.
The expected responses are:
(a)(i) A lightning conductor is a long metal rod/ bar with a pointed end placed above a (tall) building and connected by a thick cable attached to a metal plate buried in the ground.
(ii) Positive charges are repelled to the charged cloud to neutralize the charges in it However, if enough charges are not repelled to neutralize the charged cloud and a flash of lightning occurs, the current is conducted to the earth through the copper plate thereby protecting the building
(b)
(c) F1 =
F2 =
= = 2
= =
= 3.54 x 10 -2 m
