Domestic wiring and protection

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04 Magnetic

DOMESTIC ELECTRIC CIRCUITS (OR DOMESTIC WIRING)

Electricity is generated at the power station. It is brought to our homes by two thick copper wires or aluminium wires fixed over tall electric poles (or by underground cables).

The electricity from the mains is supplied to the houses using a three-core wiring. They are

o       The Live wire
o       The neutral wire and
o       The earth wire

Live Wire: It is at a high potential of 220 volts. The live wire has red insulation

Neutral wire: It is at the ground potential of zero volt. The neutral wire has black insulation covering.From the electric pole situated in our street, two insulated wires L and N come to our house. In India, the potential difference between the two wire is 220V.

The Earth wire: It is a safety measure and does not affect the supply in any way. The green earth wire is connected to a metal plate deep in the earth.

 

There are two separate circuits in a house, the lighting circuit with a 5 A fuse and the power circuit with a 15 A fuse.

EARTHING OF ELECTRICAL APPLIANCES

  • Earthing of an electrical appliance means connecting the metallic body of the powered appliance to the earth through the earth wire.
  • It is a safety measure which ensures any leakage of current to the metallic body of the appliance.
  • This is done by keeping the potential of metallic body equal to that of the earth (zero volt) and the user may not get a severe electric shock by means of a metal wire called “earth wire”.

SHORT CIRCUIT

  • If due to defective or damage wiring, the live and neutral wires come in direct contact, the resistance of the circuit becomes almost zero and an extremely large current flows through the circuit. This is called short circuiting.
  • Appliances can be protected from short circuiting by using an electric fuse in live wire.

OVERLOADING

  • If the current drawn from the mains exceeds the safety limit (5 A for domestic line and 15 A for power line), then this is known as overloading.
  • A circuit can be protected from overloading by using an electric fuse.

ELECTRIC FUSE

  • It is a safety device to protect an electric circuit from overloading or short circuiting.
  • It is a piece of wire of a material of low melting point which is connected to the live wire in the circuit. A fuse wire is connected in series in the electric circuits.
  • When an excessive current flows, the fuse melts and the circuit is broken.
  • Fuse wire is made of pure tin or tin-copper alloy, having low melting point, which melts and breaks the circuit if the current exceeds a safe value.
  • The fuse wire must have proper thickness which depends on the maximum current which the household wiring can safely carry.

MAGNETISM IN HUMAN BEINGS

  • The two main organs of the human body where the magnetic field produced is quite significant are the heart and the brain.
  • The magnetism produced inside the human body (by the flow of ionic currents) forms the basis of a technique called Magnetic Resonance Imaging (MRI) used to obtain images (or pictures) of the internal parts of our body.

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