Physics
An appliance with a metal covering, rated at 2 kW, 220 V, is to be connected in a circuit. Given below are four diagrams (P, Q, R & S) depicting different circuit configurations.
(a) Identify the safest circuit.
(b) Write two reasons, supported by mathematical calculations, where applicable, to justify your choice.
Household Circuits
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Answer
Given,
- Power rating (P) = 2 KW = 2000 W
- Voltage rating (V) = 220 V
(a) The safest circuit is S.
(b) There are two criteria to choose the circuit S :
- It is earthed so that in the case short circuit all the excess current can flow to earth without harming the person.
- The current in the supply should be less than or equal to the current rating of the fuse.
So, current in the circuit = = 9.09 A
Circuit P
As the circuit is not earthed so it is not safe.
Circuit Q
- Circuit is earthed properly.
- Current in the circuit is 9.09 A but it has fuse which has current rating of 8 A so it will get damaged and hence someone can be hurt.
Circuit R
- Circuit is not earthed properly so it is not safe.
- Current in the circuit is 9.09 A and it has fuse which has current rating of 10 A.
Circuit S
- Circuit is earthed properly.
- Current in the circuit is 9.09 A and it has fuse which has current rating of 10 A.
So circuit S satisfy all the necessary criteria for a safe circuit.
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