Question

Calculate the values of effective resistance in each case.

(A) What is the function of fuse in an electric circuit?

(B) How is the SI unit of electric energy related to its commercial unit? 

(C) What would be the rating of the fuse for an electric kettle which is operated at 220V and consumes 500 W power?

Answer 1

(A) A fuse wire is a safety wire connected in series with the live wire.  Fuse wire melts down in case of supply of large current supply or malfunctioning in the electric connections due to the following Characteristics.
            Characteristics:

1.  High resistivity
2. Low melting point.

(B) The SI unit of energy is Joules and the commercial unit of electric energy is kWh.

1 kWh = 1000 W × 1 hour

= 1000 W × 3600 s

= 36 × 10⁵ Ws

= 3.6 × 10⁶ J

(C) Given power:500 watt
Voltage=220 Volts
I=P/V
=500/220
=2.27 A
Rating of fuse wire will be 2.5 or 3