Question

A circuit consists of a battery, a metal wire, an ammeter and a switch connected in series. The switch is closed and the ammeter reading noted. The metal wire is now heated.

1. State the observation made on the ammeter reading and give a reason for your answer 
2. State the purpose of a fuse in a circuit. 
3. An electric heater is made of wire of resistance 100Ω and 2400 V mains supply. Determine
   • Power rating of the heater 
   • Current flowing in the circuit 

Answer 1

1. The ammeter reading decreases. The resistance of the metals decreases with increase in temperature.
2. A fuse open/breaks an electric circuit when current flow exceeds certain amount. 
3.    
   • P= v2/R = 2402/100=     576W 
   • I= p/v = 576/240