Electric current and its effect CLASS-8

Electric current
HEATING EFFECT OF CURRENT
MAGNETIC EFFECT OF CURRENT
ELECTROMAGNET
ELECTRIC BELL
ADVANTAGE OF HEATING EFFECT
DISADVANTAGE OF HEATING EFFECT
SYMBOLS OF ELECTRIC COMPONENTS
MINIATURE CIRCUIT BREAKER (MCB)
ELECTRIC FUSE

1. Friday, December 1, 2017 1
CREATED BY – RAVI PRAKASH SINGH
FOR CLASS – VII
SUBJECT – PHYSICS (SCIENCE)

2. 
Different form of energy are
Heat energy
Light energy
Sound energy
Mechanical energy
Magnetic energy
Electrical energy
CHEMICAL ENERGY

These different form of energy can be transferred from one
form to another. It play important role in day to day life
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DIFFERENT FORM OF ENERGY

3. 
Electric component Diagram Symbol
1)Electric cell



2)Electric bulb



3)Switch in OFF position

4)Switch in ON position

5)Battery


SYMBOLS OF ELECTRIC COMPONENTS
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+ -
+ -

4. 
Electric component Diagram Symbol

6)Wire


7)Fuse


8)Ammeter


9)Voltmeter
SYMBOLS OF ELECTRIC COMPONENTS
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5. 
It has a positive terminal and a negative terminal. The
symbol of an electric cell has a longer line and a shorter
line. The longer line is the positive terminal and the
shorter line is the negative terminal.

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Electric cell :-
+ -

6. 
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Battery
A battery is a combination of two or more cells. In a battery
the positive terminal of one cell is connected to the
negative terminal of another cell. Devices like torches,
transistors, toys, TV remote controls use batteries.
Connecting cells together
Cell holder

7. 
A SIMPLE ELECTRIC CIRCUIT
A simple electric circuit can be made by using a cell,
electric bulb, switch and wires.
The bulb glows only when the switch is in the ON position
and the circuit is closed.
Open electric circuit
Closed electric circuit
An electric circuit
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8. 
When electric current flows through a wire, the
wire gets heated. This is called the Heating
effect of electric current.
Factor affecting the amount of heat produced
are as follow:
1)The strength of Electric current
2)Resistance of the heating element (Nature of
material, Length & thickness of wire)
3)Time for which electric current flow


HEATING EFFECT OF ELECTRIC CURRENT
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9. 
Make an electric circuit as shown in the figure. Take a 10 cm long
nichrome wire and tie it between the two nails. Switch on the current.
After a few seconds touch the wire. The wire feels hot. Then switch off
the current. After a few seconds touch the wire again. It does not feel
hot. This shows that when electric current flows through a wire, it gets
heated.
Nichrome wire get heated but connecting wire practically not heated
because resistance of connecting wire is negligible but resistance of
Nichrome wire & the bulb are not negligible.
Replace the cell by battery, now nichrome wire gets Red-hot more
quickly i.e. heat produced increase with increase in the strength of the
current.
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Activity : FOR HEATING EFFECT OF ELECTRIC CURRENT
Nichrome wire
Nail

10. 
Advantages of the heating effect of electric currents are:
1.Making electric light like bulbs, CFLs.
2.Making Toaster and electric heater for cooking food.
3.Making room heaters to keep a room warm during cold
seasons.
4.Making electric fuses
5.Making other electrical appliances like Electric Iron,
Immersion Rod, Electric Kettle, Hair Dryer, Geyser, Water
heating coils, space heater etc.


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ADVANTAGE OF THE HEATING EFFECT
Electric heater Electric room heater Electric iron Electric kettle

11. 
Disadvantages of the heating effect of electric currents are:
1)It reduces the life of several components in a circuit.
2)Heat produced causes wastage of energy
3)It causes short circuits and explosions.
4)It causes fires and circuit failures.
5)It is dangerous if electrical appliances are not handled
properly.
6)Additional cooling systems and heat sinks need to be
added to circuits to counter the effect of heating, which
adds to the cost.
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DISADVANTAGE OF THE HEATING EFFECT

12. 
Nichrome (an alloy of nickel & chromium) is used for
making wires of heating coils because
1)It has high melting point
2)It has high resistivity
3)It can remain Red Hot for long time without getting oxidised
or burning out.
Tungsten wire is used for making metal filament of an
electric bulbs because
1)It has a very high melting point
2)When current passes through it , it becomes White Hot and
glows brightly for a long time
3)It is quite stable & has long life vis–a-vis (आमने सामने,
प्रतिकूल unfavourable) burn out or possible oxidation.
Note: Nichrome is used for getting heat energy.
Tungsten is used for getting light energy.

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General Fact

13. 
ELECTRIC FUSE
Electric fuse is a safety device used in electrical circuits which
protects the electrical circuits and appliances and prevents fires.
Electrical fuse is used in all electrical circuits in buildings.
Electric fuse has a wire which melts quickly and break when
large electric current flows through it.
Fuse used in
buildings
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14. 
Fuses are useful when the current in the circuit exceeds the
specified maximum safe value of circuit due to
1)Short Circuit - Touching Of Wires Leads To Short Circuiting.
2)Overload – More than one appliance/device connected to
single socket.
3)Insulation Break Down – the wires may become overheated &
result in a fire
In above case fuse wire get too hot & even melt down and it break
The amount of current required to melt down of fuse wire depends
on the nature of material used (not on its length).
The melt down action of a fuse wire depends upon its current
rating.
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USES OF FUSE

15. 
A Miniature circuit breaker is an automatically operated electrical
switch designed to protect an electrical circuit from damage caused
by excess current, typically resulting from an overload or short
circuit or imperfect design.
Its basic function is to interrupt current flow after a fault is detected.
MCBs ranges from 1 KA to 10 KA with 1-pole, 2-pole, 3-pole or 4-
pole configurations.

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MINIATURE CIRCUIT BREAKER (MCB)

16. 
MAGNETIC EFFECT OF ELECTRIC CURRENT
When electric current flows through a wire, it
behaves like a magnet. This is called magnetic
effect of electric current.
The magnitude of magnetism produced by an
electric current in a wire
1)Increases with an increase in the strength of
electric current
2)Decreases with an increase of distance from
the wire
Friday, December 1, 2017 RAVI PRAKASH SINGH 19

17. 
Take the cardboard tray from a match box. Wind an
electric wire a few times around the cardboard tray. Place
a small compass needle inside it. Connect the free ends of
the wire to an electric cell through a switch. When the
switch is ON, the compass needle deflects. When the
switch is OFF, the compass needle comes back to its
original position. This shows that when electric current
flows through a wire, it behaves like a magnet.

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Activity :- To check magnetic effect of current

18. 
ELECTROMAGNET
An electromagnet is a type of magnet in which the magnetic field
is produced by an electric current. The magnetic field disappears
when the current is turned off. Electromagnets usually consist of
insulated wire wound into a coil.
The strength of an electromagnet can easily be changed by
changing the amount of electric current that flows through it or
changing the number of turn.
EX- Electromagnets are found in motors, tape decks, hard
drives, VCRs and tons of other devices.
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19. 
Wind a piece of insulated wire around an iron nail in the
form of a coil. Connect the free ends of the wire to an
electric cell through a switch. Place some pins near the
nail. When electric current is passed, the iron nail
becomes a magnet and attracts the pins. When electric
current is switched off, the nail loses its magnetism.
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Activity :- ELECTROMAGNET

20. 
The electric bell is a small electrical devices that convert
electrical energy into mechanical energy in the form of sound.
An electric bell contains an electromagnet, consisting of coils
of insulated wire wound round iron rods. When an electric
current flows through the coils, the rods become magnetic and
attract a piece of iron attached to a clapper. The clapper hits
the bell and makes it ring
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ELECTRIC BELL

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