Page 50 - Innovator's Science-8

Construction of an electric bell: It consists of a U-shaped electromagnet, a
Science soft iron armature or strip, a contact screw, a hammer (striker), the bell or
Bytes

gong and a switch. The armature is supported by a spring, which allows it to
Testimony
Temporary vs Permanent move to-and-fro. The hammer attached to the armature can also move to-
Magnets and-fro and strike the gong. When
An electromagnet is a Iron rod
type of temporary the terminals T and T are Bell
magnet, because its connected to a battery and the
magne sm appears only switch is pressed, current flows
while electric current Spring
flows through it. In through contact points via the
contrast, a permanent electromagnet.
magnet retains its Switch
magne sm all the me. Working of an electric bell: When
Voltage
The main advantage of an the doorbell is pressed, the switch
electromagnet is that its
strength can be easily closes and current flows through the
controlled by changing contact points to the
the amount of current or electromagnets. Thus, the U-shaped
the number of turns in
the coil. Permanent electromagnet is magnetised and it
magnets are useful in attracts the armature towards it.
compasses and door
latches, while Consequently, the striker strikes the
electromagnets are gong producing sound. The moment Voltage
preferred in electric bells, this happens, the contact of the Working of an electric doorbell
motors, and cranes. Both
types of magnets show attached spring with the screw is
how electricity and broken, that is, the circuit is broken. As a result, the current stops flowing and
magne sm are closely
linked, yet their the electromagnet is demagnetised. Due to this action of the spring, the
behaviour and uses are armature comes to its previous position, that is, comes in contact with the
quite different.
screw and the circuit is again completed. Thus, as long as the bell is pressed,
the same process is repeated to produce ringing sound.

DOES A CURRENT CARRYING WIRE GET HOT?

When we use a special wire called nichrome wire to see what happens
when electricity passes through it. The wire is tied between two nails fixed
on a piece of cardboard, and the setup is connected to a battery through a
switch. When the switch is off, the nichrome wire feels normal to touch. But
when you turn the switch on for a short time and then off again,

the wire becomes warm or hot. This shows that when an electric
current flows through a wire, it produces heat, which can be felt in
the wire.

When electric current flows through a wire, it does not move
freely; the wire opposes its flow to some extent, which is called
Heating effect in a wire
resistance. Due to resistance, some electrical energy changes into
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Science-8