Heating effect, Lighting effect, Magnetic effect, Electromagnetic Induction, Motor effect, Dynamo, Generator, Motor and Transformer

1. Heating effect of Current
• When electric current is supplied to a purely resistive conductor, the energy
of electric current is dissipated entirely in the form of heat and as a result,
resistor gets heated. The heating of resistor because of dissipation of
electrical energy is commonly known as Heating Effect of Electric Current.
• Some examples are as follows:
• When electric energy is supplied to an electric bulb, the filament gets
heated because of which it gives light. The heating of electric bulb happens
because of heating effect of electric current.
• When an electric iron is connected to an electric circuit, the element of
electric iron gets heated because of dissipation of electric energy, which
heats the electric iron. The element of electric iron is a purely resistive
conductor. This happens because of heating effect of electric current.
• Factor affecting the amount of heat produced are as follow:
• The strength of Electric current
• Resistance of the heating element (Nature of material, Length & thickness
of wire)
• Time for which electric current flow
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2. Cause of heating effect of electric
current
• Cause
• Electric current generates heat to overcome the resistance offered by the
conductor through which it passes. Higher the resistance, the electric
current will generate higher amount of heat. Thus, generation of heat by
electric current while passing through a conductor is an inevitable
consequence. This heating effect is used in many appliances, such as
electric iron, electric heater, electric geyser, etc.
• Joule’s Law of Heating
• P=VI
• H=I2Rt
• The second expression is known as Joule’s Law of Heating, which states
that heat produced in a resistor is directly proportional to the square of
current given to the resistor, directly proportional to the resistance for a
given current and directly proportional to the time for which the current is
flowing through the resistor.
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3. Heating element/devices
• The devices which are used for heating purpose
or to convert electrical energy into heat energy is
called heating devices.
• Nichrome (an alloy of nickel 60% & chromium
40%) is used for making wires of heating coils
because
• It has high melting point
• It has high resistivity
• It can remain Red Hot for long time without
getting oxidized or burning out at about 900 oC.
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4. Lighting effect of Current
• When electric current is passed through a conductor, it
becomes very hot due to which it emits light. This is
called lighting effect of electric current. For
example: electric bulbs, fluorescent lamps, etc.
• The devices which are used to convert electrical energy
into light and heat energy are called lighting devices.
• Tungsten wire is used for making metal filament of an
electric bulbs because
• It has a very high melting point
• When current passes through it , it becomes White Hot
and glows brightly for a long time
• It is quite stable & has long life
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5. Filament Lamp
• Current is passed through a
filament (tungsten).
• The temperature of the wire is
raised and light as well as heat
energy is emitted.
• Higher the temperature,
higher is the amount of light
energy radiated.
• Thus, lamp filament should be
of such a material whose
temperature can be raised
quickly without causing any
damage to it up to 2900 *C
• Tungsten has a high melting
point (3400*C) and high
resistivity.
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6. Filament Lamp
• Chemically inert gas is filled in
the bulb to prevent oxidation
and lowering of filament
temperature.
• Usually nitrogen or argon gas
is used and sometimes a
mixture of 85% of argon and
15% of nitrogen is also used.
• It is not more efficient.
• It converts only 10% of
electrical energy into light and
remaining 90% of the energy is
converted to heat.
• The life time is about 1000 hrs.
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7. Fluorescent Lamp
• An electric lamp in which
fluorescent powder is used to
convert electrical energy into
UV rays and then to light.
• A fluorescent lamp consists of a
glass tube filled with a mixture
of argon and mercury vapor.
• Inner wall are coated with
fluorescent powder like zinc or
cadmium silicate or calcium or
magnesium tungstates that
gives off electrons easily.
• It consists of two electrodes at
two ends. When the power is
switched on, the cathode is
heated and it emits electrons as
the gas gets ionized.Anjan Nepal

8. Fluorescent Lamp
• The electrons or ions move
towards anode. While moving,
they collide with the mercury
vapor and produces ultraviolet
radiation.
• The inside of the tube is coated
with phosphors, substances that
absorb ultraviolet radiation and
fluorescent powder (reradiate the
energy as visible light).
• The UV rays strike the atoms of
fluorescent powder to produce
visible light.
• It converts 30% electrical energy
in to light and remaining 70% in
to heat.
• The life time is about 10,000 hrs.
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9. CFL
• CFLs, or compact fluorescent light bulbs,
are simply miniature versions of full-sized
fluorescents and are available is many
different shapes and sizes.
• They are functionally identical to linear
fluorescent bulbs.
• Both are gas-discharge lamps that use
electricity emitted from cathodes to excite
mercury vapor contained within the glass
envelope.
• Phosphors and a noble gas such as argon
are also contained within the glass
envelope.
• The mercury atoms produce ultraviolet
(UV) light, which in turn causes the
phosphors in the lamp to fluoresce or glow,
producing visible light
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10. LED
• An LED lamp or LED light
bulb is an electric light for use
in light fixtures that produces light
using one or more light-emitting
diodes (LEDs) or semiconductor
light source.
• They have special diodes which
emits light. This is based on
electroluminescence. When
current supplied, electrons release
energy in the form of photons.
• LED lamps have a lifespan many
times longer than
equivalent filament lamps, and are
significantly more efficient than
most fluorescent lamps.
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11. Magnetic Effect
• The phenomenon due to which a magnetic field is produced
around a current carrying conductor is called magnetic
effect of current.
• When electric current passes through a wire, the current-
carrying wire behaves like a magnet. This is called
the magnetic effect of current.
• The magnetic effect of electric current is known as
electromagnetic effect. It is observed that when a compass
is brought near a current carrying conductor the needle of
compass gets deflected because of flow of electricity. This
shows that electric current produces a magnetic effect.
• The magnetic effect of current is utilized in making
electromagnets, electric bells, telephone
instruments, electric fans, radio, televisions, electric motors,
loudspeakers and toys, etc.
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12. Solenoid is the generic term for a coil of wire used as an
electromagnet. It also refers to any device that converts electrical
energy to mechanical energy using a solenoid. The device creates a
magnetic field from electric current and uses the magnetic field to
create linear motion.Anjan Nepal

13. Electromagnet
• Electric current is passed
through a solenoid of
copper wire in an iron core
gets magnetized called
electromagnet.
• It is a temporary magnet
• It shows magnetic
property only when
electric current flows
through solenoid.
• It converts electrical
energy into magnetic
energy.
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16. Electromagnet
Factors affecting strength of electromagnet
• Amount of the electric current
• Number of turns of coil in the electromagnet
• The material of the core on which the windings of
wire is made
Therefore, strength can be increased by the
followings:
• Increasing the number of turns of coil in solenoid
• By increasing the amount of current passing
through the coil
• By placing soft iron core
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19. Electric Bell
• The bell made of temporary magnet/electromagnet which produces
sound only when electric current is on.
• Working mechanism
• The switch is pressed and current flows through the circuit.
• The electromagnet is powered and generates a magnetic field that
attracts the iron strip towards it.
• The striker strikes the gong (bell).
• When the striking arm strikes the gong, the contact is broken and
current stops flowing through the circuit.
• This causes the electromagnet to lose its magnetic field.
• The connected spring arm returns the striker to its original rest
position.
• The contact is restored and current flows through the circuit
(provided the main switch is still pressed).
• The process is repeated from the beginning.
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21. Electromagnetic Induction
The production of an electromotive force (i.e. voltage) across an electrical
conductor in a changing magnetic field or the induction of an electromotive
force by the motion of a conductor across a magnetic field or by a change in
magnetic flux in a magnetic field.
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22. Electromagnetic induction
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23. Bicycle Dynamo
• Principle: It is based on the
principle of electromagnetic
induction.
• Construction: It consists of a
wheel and axle connected to a
permanent magnet (rotor).
• The magnet is cylindrical in
shape with poles on opposite
sides.
• A soft iron core with the coils of
wire is fixed and it does not
rotate.
• The poles of core are concave
shaped to fit closely round the
rotor.
• Working: When the magnet
rotates, the magnetic lines of
force is changed in the coil and
electric current is induced in
the coil.
A device which converts mechanical energy
into electrical energy is called dynamo.
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24. Generator
• It is a device which converts
mechanical energy into electrical
energy.
• Principle: It is based on the
principle of electromagnetic
induction. Whenever the
magnetic flux passing through a
closed circuit is changed in the
coil, emf will be induced in it. As a
result, current flows in the coil.
• Construction: It has a rectangular
coil of wire which is rotated in the
magnetic field between the poles
of a U shaped permanent
magnet. This magnet is called the
field magnet.
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25. Generator
• The ends of the coil are
connected to two slip rings
mounted on the coil spindle.
• There are two carbon brushes
which are made to press
lightly against the slip rings.
• As the coil rotates, its sides
come across the magnetic flux
and a current is induced in it.
• The induced current flows in
the circuit through the carbon
brushes. current flows in the
coil. tools
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26. Strength of Induced Current
• Bicycle dynamo is very small generator which produces
very small current.
• Generators are used to generate electricity from
hydropower and nuclear power produces very large
current.
• The induced emf of generator or dynamo can be increased
by following ways:
• By increasing the number of turns of coil
• By increasing the strength of the magnetic field
• By increasing the speed of rotation of magnet near the coil
or increasing speed of rotation of coil in the magnetic field
• By decreasing the space between the magnet and the coil
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27. (Direct current) (Alternating current)
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30. Electric motor
• An electric motor is a rotating
device which converts electric
energy into mechanical energy.
• An electric motor brings about
rotational motion in domestic
appliances such as electric fans,
washing machine, mixer, grinder,
computer, MP3 player, electric
water pump, etc.
• Principle: It is based on the
principle of motor effect. When a
current carrying conductor is
placed in a magnetic field,
experiences a force. As a result,
motion in conductor occurs
• Types: There are two types of
electric motor that we use in our
daily life.
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31. Electric motor• AC motor that uses AC supply, e.g.,
the motor of a fan, washing machine,
etc.
• DC motor that uses DC supply, e.g.,
the motor of battery operated toys.
• Construction and working
• It consists of coils placed between the
poles of a strong magnet.
• The wires from the coil are connected
with two split rings. When the current
is passed through the coil, a magnetic
field is set up around it.
• This magnetic field interacts with the
magnetic field of the magnet. As a
result, the coil experiences a force due
to which it begins to rotate.
Armature (Coil)
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33. Mutual Induction
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36. Transformer
• Construction: It consists of three
vital parts i.e., soft iron core,
primary Com and secondary coil.
• Soft iron core consists of a
rectangular frame made from thin
laminated sheets of soft iron. Each
sheet is laminated by varnish or
shellac.
• The lamination of the soft iron core
is done in order to prevent the loss
of energy due to eddy current
which would flow in the core.
• The sheets are held tightly by
clamps.
• Soft iron core has very high
magnetic permeability. As a result,
it concentrates magnetic lines of
force and reduces energy loss.
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37. Transformer
• One coil is supplied with
alternating current and is called
primary coil
• The voltage supplied in primary
coil is called primary voltage.
• The coil of the transformer from
which electric current is tapped
out is called a secondary coil.
• The voltage of the secondary coil
is called the secondary voltage.
• The current supplied in the
transformer is called input
current and the current produced
from the transformer is called
output current.
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38. Transformer
• There is an important relationship between the ratio of the number
of turns of coil in the primary and the secondary winding with the
primary and secondary voltage which can be stated as:
• or
• The important thing we must know before making a transformer is
that the number of turning in any coil should be about 1000 for
greater efficiency and durability. If the number is less needed, the
transformer will be heated and energy loss takes place. If the
number too less, short circuit will occur.
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40. Types of Transformer
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41. Transformer
• Advantages:
• Converts high voltage of alternate current into
low voltage and vice versa
• Responsible for long distance transmission of
alternating current (AC) through aluminium
wire
• It prevents circuit from damage
• Electric accident prevention
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43. Battery Charger
• A battery charger, or
recharger, is a device used to
put energy into a secondary
cell or rechargeable battery
by forcing an electric current
throughit.
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44. Inverter
• A power inverter,
or inverter, is a power
electronic device or circuitry
that changes direct current
(DC) to alternating current
(AC).
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45. Electricity consumption
• In a house or a building, there may be several appliances like electric
bester, bulb, TV set, rice cooker, refrigerator, etc.
• The total energy consumed by all of the house appliances is summed up
by an electrical device called watt meter.
• The watt meter is kept between the power line coming through pylon and
the main electric switch in the house.
• Let an appliance has its power rating 'P' watt. If an appliance is used for
time 't' seconds, the energy consumed 'E' by the appliance is given by
• E =P x t (joules)
• This electrical energy consumed by the appliance is in fact the work done
by the power line on the appliance.
• Hence, we can also write as:
• Electrical energy consumed (E) = Work done by the current = Power x Time
• If there are ‘n’ number of appliances, then
• Energy consumed, E = Power x Time x number of devices = P x T x N
• Hence, it is clear that the electrical energy consumed by an electrical
appliance is simply given by the product of the power rating of the
appliance and the time for which the appliance has been in use.
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46. Commercial Unit
• The commercial unit of electrical energy is called Kilowatt-
hour (kWh).
• 1 kWh is defined as the energy consumed by electrical
appliance having power rating of 1 Kilowatt in one hour.
• 1 kWh = 3.6 x 106 joule
• Cost of total energy consumption = Total kWh x Rate of one
unit
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