Page 123 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

v When electric current is passed through a wire, it gets heated. This is called the heating

effect of electric current.
v The amount of heat produced in a wire depends on the material, length & thickness of the

wire.
v Resistance means the hindrance or opposition to the flow of electric charge.
v More the thickness of the wire lesser is its resistance & lesser will be the heat produced.

On the other hand, longer the wire, more is its resistance & higher will be the heat produced
in it.

v An electric fuse is a safety device to prevent damage to an electric circuit when excess
current flows through it. it consists of a fuse wire made up of an alloy of tin & lead, having

a low melting point. This is why it melts when high current flows through it & breaks the
electric circuit.

v MCB (Miniature Circuit Board) is a switch which automatically trips off when it detects
excess current in the circuit.
In 1820, Hans Christian Oersted noticed that when electric current is passed through a wire,

it behaves like a magnet. This is known as the magnetic effect of electric current.
v A coil which behaves like a magnet when electric current passes through it, is called an

electromagnet.
v A coil with many circular turns of insulated copper wire is known as a solenoid.

An electric bell makes use of the principle of an electromagnet.
In 1910, American physicist, William David Coolidge, invented the ductile tungsten filament

for bulbs.

Exercise

A. Tick (3) the correct answer.
1. Electric current is conducted through ........................ .

(a) Kerosene (b) Pure water (c) Gold (d) oil

Ans: (c)
2. The heat generated in a wire due to the passing of electric current through it depends

on .................... .

(a) Material of the wire (b) Length of the wire
(c) Thickness of the wire (d) All of these

Ans: (d)
3. If the switch in an electric circuit is in the OFF position, it is called ........................ .

(a) Short circuit (b) Open circuit (c) Closed circuit (d) None of these

Ans: (b)

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