Physics
To which wire is the metallic case of an electric appliance connected? Give the reason?
Answer
The metallic case of the appliance should be properly earthed by connecting it to the earth wire.
When the live wire of a faulty appliance comes in direct contact with it's metallic case due to break of insulation after it's constant use (or otherwise), the appliance acquires the high potential of the live wire.
A person touching the appliance will get a fatal shock because current flows through his body to the earth. But if the metallic case of the appliance is properly earthed, then as soon as the live wire comes in contact with the metallic case, a heavy current flows to the earth through the case of the appliance (since the metallic case has almost zero resistance) and the fuse connected in the circuit of appliance blows off, and the appliance gets disconnected from the mains supply.
Thus the person touching the appliance does not get any shock and the appliance is also saved from being damaged.
Related Questions
The diagram in figure shows a three pin plug. Label the three pins.
(a) Why is top pin thicker and longer than the other two?
(b) Why are the pins splitted at the ends?
It is dangerous to connect the switch in the neutral wire. Explain your answer.
For earthing an electrical appliance, one has to remove the paint from the metal body of the appliance where the electrical contact is made. Explain the reason.
(a) The earthing of an electric appliance is useful only if the fuse is in the live wire. Given the reason.
(b) Name the part of the appliance which is earthed.