SUBJECT – SCIENCE GRADE –VII
TOPIC- ELECTRIC CURRENT AND ITS EFFECTS
1. Define the following termsa. Electric current – The flow of electricity along a path is called
electric current.
b. Electric circuit-When electricity flows through a closed path
is called electric circuit.
c. Cell- In an electric circuit the source of energy is supplied by
the cell.
d. Battery- The combination of two or more cells is called
battery.
e. Electrical appliances –Electric appliance are devices that uses
electricity to perform a function.
f. Standard symbols- A circuit can be represented by a set of
symbols using circuit diagrams.
2. Draw the symbols of some electric circuits
3. Write a short note on heating effects of electric current.
Heat is produced due to the resistance of moment of electrons
through certain materials like tungsten and nichrome . The
work done by the electrons to force their way through certain
materials is given out in the form of heat energy .
4.Name some electrical appliances where heating effect of
electric current is used.
Toasters, electric kettle, microwave ovens, geysers and electric
iron.
5. What are the factors on which the amount of heat produced
by electric current carrying conductor depends upon?
1. Material of a conductor- Tungsten and nichrome wire add
more resistance.
2. Length and thickness of the conductor- Thick and long wires
produced high resistance.
3. Amount of current flowing through the wire –More the
strength of electric current, more is the resistance provided.
6. What is electric fuse?
Electric fuse is a safety device in an electric circuit. When a very
high current flows through the circuit, the fuse wire gets
heated, melts and breaks the electric circuit.This prevents fire
and damage to the various electrical appliances.
7. What is MCB or Miniature circuit breakers?
It is a safety device (a switch) which automatically turns off
when electric current in a circuit exceeds the safety limit. It can
be reset by pressing a switch after repairing a fault.
8. What causes short circuit?
Due to overloading of wire, the insulation wire melts and
undergo wear and tear. This causes live wire to come in contact
with neutral wire and a large amount of current flows through
them. Heat is produced and this leads to fire. This causes short
circuiting.
9. What is electromagnet?
A current carrying coils of an insulated wire wrapped around a
piece of iron is called electromagnet.
10. How can we increase strength of an electromagnet?
1. By increasing number of loops in the coil.
2. By increasing amount of current flowing through the circuit.
11. What are the uses of an electromagnet?
1. They are used in cranes to lift heavy loads.
2. They are used to separate magnetic substances from the
junk.
3. Doctors use tiny electromagnets to take out small pieces of
magnetic materials from human body parts.
4. Many toys have electromagnets inside them.
12. Explain working of an electric bell with neat and labelled
diagram?
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