Which test can best detect the presence of electrical current a the needle of a compass b the bulb in an electric circuit blows c the plug of an iron is placed in the socket?

Answer 1

Here are some possible answers: a) If you hold a compass close to a wire you may see the needle move. How much it moves depends on the strength of the current flowing in the wire. If the needle doesn't move then there may be three explanations: 1) No direct current was flowing in the wire OR 2) a direct current was flowing but it was too weak to make the compass needle move OR 3) there might have been a current but it was an alternating current changing so fast that the needle did not seem to move.

b) If the bulb in an electric circuit was lit but then blows, it may mean one of two things 1) the current was switched off so the bulb went out OR 2) the bulb just died, in which case any current that was flowing in the bulb's circuit would stop. c) when the plug of an iron is placed into a socket, if it warms up then a current must be flowing from the socket to the iron. But before the iron was plugged-in, no current was flowing. Now you work out which of those answers to this question is the right one!

Answer 2

For detecting the presence of electrical current, a multimeter set to measure current can be used for all three situations. It can measure the current passing through the needle of a compass, the current that caused the bulb in an electric circuit to blow, and the current drawn when the plug of an iron is placed in the socket.