NCERT book content class 7th

1. mm
Electric current and its effect
SNEHA
Integrated B.Sc. – B.Ed.(Medical)

3. Electronic component
• These elements helps in functioning of electric
circuit.
• A battery is defined as a combination of two or more
cells. In a battery, negative terminal of one cell is
connected to the positive terminal of the next cell
and so on.

4. Application
Batteries are used in several devices such as
• toys
• Remote control
• torches
• transistors.

5. HOTS
Q. Paheli and boojho
wonder whether the
batteries used in
tractors, trucks &
inverters are also made
from cells. Then why is it
called a battery? Can
you help them to find the
ans. To question?
Ans. The battery used in
tractors, truck & inverters
is a combination of several
cells. The cell are not dry
cells. These are the several
sets of plates & each set of
plates acts like a cell.

6. I want to cook rice. Can you tell me what
things are required form making rice?
Students reply water, rice, cooker, gas.
 if the gas is finished, can we cook food without
gas?
 Likewise in the circuit diagram

7. If I have wires and bulb but I don’t have cell. so
the bulb will glow? And the electric circuit is
complete without cell?

8. Open circuit
• When the key is switched off or opened the
circuit is said to be incomplete.

9. Close circuit
• When the key is switched on or closed the
circuit is said to be complete.

10. Filament
• Bulb has a wire present inside is called filament.
• When current passes through the filament it closed.

11. What happens when the filament of
a bulb breaks?

12. Heating effect of electric current
• When an electric current passes through a
wire & the wire get heat up.
• Heat produced in wire depends upon:
- material, length, thickness of wire.
e.g. = geyser, toaster, heater

13. All these elements produce a high
amount of heat when electricity
passes through them. However, this
amount can change depending upon
the requirements of the device. This
is so because they contain a coil of
wire known as an element.
Depending upon the amount
of heat required by such
appliances different types,
sizes and length of wire are
used in them. Some virus can
break down or melt as they
get heated.

14. Do you think is there any drawbacks of
these appliances?
Ans. The other major
disadvantage of
electrical energy is that
it's relatively easy to
become disconnected
from this power source.

15. If appliances over heated then they may get
damage or even catch fire .every
appliances in our house is effected by
unwanted high electric current there is a
limit . but if current excess that limit> heat
up > fire.
Is there any way to prevent that happening?
We can use fuse
to prevent this
happening.

16. What are these?
Where we use these?

17. Electric fuse
• It is a device that use to prevent damage which caused by
excess of electric current.
• excess current passed through a wire it can melt or
break.
• Fuse wire made up of metal or alloy which has low
melting point.
• prevent a short circuit for fire due to high electric
current.
• Different types of fuses are used for different devices and
some are also available for houses as well.

18. MCB
• Miniature circuit breaker is used buildings.
• instead for fuses.
• These switches which automatically turn off when
current exceed.
• You can turn them on & circuit is complete again.

19. fuse wire is made up of metal
or alloy but what if it made
up of aluminium.
Because Aluminium
has high resistance
& high melting
point.