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Class 10, Science, Chapter-12, Lecture-3, Domestic Wiring (Notes)

Colour coding for Domestic Wiring:

RED insulation cover for LIVE wire (positive)
BLACK insulation cover for NEUTRAL wire (negative)
GREEN insulation cover for EARTH wire

ROLE OF EARTH WIRE:

The earth wire connects the metallic body of an appliance to the earth and facilitates easy flow of current in case of leakage of current.

This keeps the potential of the metallic body equal to that of the earth and prevents the user from severe shock.

Necessity of Earthing Metallic Appliances:

The earth wire connects the metallic body of an appliance to the earth and facilitates easy flow of current in case of leakage of current.

In the absence of an earth-wire, if leakage of current takes place, the current will pass through the body of the person who touches the metallic part and will give an electric shock to the person.

So, it is necessary to earth metallic appliances.

Reasons for Parallel Connection of Appliances In Domestic Circuits:

  1. To maintain equal voltage across each appliance.
  2. To ensure that if one switch is ‘on’ or ‘off ’, the other appliances are not affected.

SHORT CIRCUIT:

The phenomenon in which the live wire and the neutral wire in an electric circuit come in direct contact and reduces the path of flow of charge is termed as short circuit.

OVERLOADING:

The flow of a large amount of current in a circuit due to short circuiting or accidental hike in voltage supply or connecting too many appliances in parallel is termed as overloading.

Cause of overloading:

  1. Short circuit
  2. Accidental hike in the supply of voltage
  3. Connecting too many appliances (in parallel) to a single socket.

CONSEQUENCE of short circuit:

Heat produced in a wire is directly proportional to square of current flowing through it. ( H µ I 2 )

A huge amount of current flows through live wire due to short circuit.

So, a huge amount of heat is generated which may lead to fire.

CONSEQUENCE of overloading:

Heat produced in a wire is directly proportional to square of current flowing through it. ( H µ I 2 )

A huge amount of current flows through live wire due to overloading.

So, a huge amount of heat is generated which may lead to fire.

ELECTRIC FUSE:

A piece of wire of a material with very low melting point which is connected in series in a live wire and breaks the circuit when flow of current exceeds safe limit, is termed as an electric fuse.

An Electric Fuse is Considered as A Safety Device.

Justification:

If the amount of current flowing through a conducting wire increases a certain limit due to short circuiting or accidental hike in voltage supply or connecting too many appliances in parallel, a large amount of heat is generated which may lead to fire.

The fuse wire melts and breaks the circuit, thus preventing the fire.

So, fuse wire is considered as a safety device.

Two safety measures commonly used in electric circuits and appliances:

  • Use of earth wire.
  • Use of electric fuse.

Effect of Magnetic Field on the speed of a charged particle:

Force(F) experienced by a charged particle(q) moving with velocity(v) in a magnetic field(B) acting at an angle ( ) to the direction of velocity is given by:

${\rm{F = qvBsin\theta }}$

${\rm{m}}{\rm{.a = qvBsin\theta }}$

${\rm{a = }}{{{\rm{qvBsin\theta }}} \over {\rm{m}}}$

For acceleration to be zero, should be 0 or 180O.

In other cases, speed of the charged particle will change.