Safety Precautions

Electricity from power stations is transmitted to homes through high voltage power lines. Electric potentials as high as 220 000 V AC are used. The electrical potential is decreased to 220 V AC with the help of step-down transformer before it enters the home. A cable containing three color-coded wires enters the home. One wire is red, one s black, and one is green. The red wires are called live wires (or positive). Another wire the the black insulation is called neutral wires (or negative). There is an electrical potential difference of 220 V AC between a red and a black wire. The earth wire, which has insulation of green color , is usually connected to metal plate deep in the earth near the house.

Fuses and Circuit Breakers:

A fuse is a safety device that acts as a switch. Fuses are connected into the circuit close to the source. As a result all the current flowing in the circuit passes through the fuse. When too much current flows, the fuse heat up sufficiently to bum out. This creates an air gap and no more current flows. A fuse wire is always connected to the live wire so that if excessive current flows through the live wire, then fuse wire melts itself and prevents the appliance from damage.

Illustration : Why a fuse is always connected in series?

Solution : A fuse is always connected in series due to the following given reasons:

A fuse is a safety device which helps in avoiding overloading and short circuit. So, they are caused due to the fact that the overall resistance in the circuit becomes quite large. So If a fuse is not connected in series, then it cannot take the load of effective resistance. So it is connected in series to provide effective safety in the circuit.

It is also connected in series so as to pass the current totally through the fuse and the electric appliance is saved.

So if it is not connected in series then during a electrical fault it will not act as a electricity-cutter and current will continue flowing causing an electric shock to the person concerned.

Circuit Breaker Panel:

At the homes, the electricity first passes through an electric meter. The electric meter records the amount of electric energy used in the home. Then the electricity enters a circuit breaker panel. In some older homes it may enter a fuse panel . In the panel there is a master circuit breaker. The master circuit breaker can be operated manually to cut off the electricity to the entire home. It opens automatically if the current exceeds the rated value. In homes that have a 100 A service, the master circuit breaker will allow up to 100 A to pass before it pops open.

Precautions to be Taken while Using Household Electrical Appliances:

A human body is a good conductor of electricity and we receive shock when the electric current flows through our body. Whenever we use electrical appliances, we must be careful to see that no part of our body comes into direct contact with a wire carrying current.

1. Always use appliances carrying ISI mark.

2. For performing any experiment in electricity use only cells and not the mains supply to your household.

3. Do not put a finger or a metallic wire in the sockets.

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Sample Questions

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Question : 1

Electricity from power stations is transmitted to homes through __________________ voltage power lines.
A. High	B. Medium	C. Low	D. None of these.
Right Option : A
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Question : 2

Which of the following precaution can be taken while using electricity ?
A. Avoid touching switches with wet hands.		B. Always use appliances carrying ISI mark.
C. Do not put a finger or a metallic wire in the sockets.		D. All of these.
Right Option : D
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Question : 3

Which of the following are correct ? (a) The electricity that is supplied is generated at electric power stations and brought to our houses by thick cables. (b) A person may get an electric shock because our body is a good conductor of electricity . (c) We should protect ourselves from dangerous and painful electric shocks.
A. Only (a) and (b) is correct .	B. Only (b) and (c) is correct .	C. Only (a) and (c) is correct .	D. All of these .
Right Option : D
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