Physics

ACKNOWLEDGEMENT
In the accomplishment of this project successfully, many

people have best owned upon me their blessings and the
heart
pledged support, this time I am utilizing to thank all the
people who have been concerned with project.
Primarily I would thank god for being able to complete

this
project with success. Then I would like to thank my
principal
Mr. DHIR SINGH and physics teacher Mrs. NEELAM
SEHGAL, whose
valuable guidance has been the ones that helped me
patch this
project and make it full proof success his suggestions and
his
instructions has served as the major contributor towards
the
completion of the project.
Then I would like to thank my parents and friends who

have
helped me with their valuable suggestions and guidance
has
been helpful in various phases of the completion of the

project.
Last but not the least I would like to thank my classmates
who have helped me a lot.
CONTENTS
1.ACKNOWLEDGEMENT
2. INTRODUCTION
3.THEORY
4.APPARATUS REQUIRED
5.CONSTRUCTION
6. WORKING
7.USES OF AC GENERATOR
8.EFFICIENCY
9.BIBLIOGRAPHY
INTRODUCTION
An electric
generator is
converts mechanical
device
that
energy to electrical
energy. A generator forces electric current to

flow through an external circuit. The source of
mechanical energy may be a reciprocating
or turbine steam engine, water falling through
a turbine
combustion
or
waterwheel,
engine,
a wind
hand crank, compressed
air,
source
energy.
of
mechanical
or
aninternal
turbine, a
any
other
Generators
provide nearly all of the power for electric

power grids.
THEORY
1.The strong magnetic field is produced by a current
flow through the field coil of the rotor.
2.The field coil in the rotor receives excitation through
the use of slip rings and brushes.
3.Two brushes are spring-held in contact with the
slip rings to provide the continuous connection
between the field coil and the external excitation
circuit.
4.The armature is contained within the windings of the
stator and is connected to the output.
5.Each time the rotor makes one complete revolution,
one complete cycle of AC is developed.
6.A generator has many turns of wire wound into the
slots of the rotor.
7.The magnitude of AC voltage generated by an AC
generator is dependent on the field strength and speed
of the rotor.
8. Most generators are operated at a constant speed;
therefore, the generated voltage depends on field
excitation, or strength.
APPARATUS REQUIRED
l 4 - 1cm x 2cm x 5cm ceramic magnet
l 1 - Magnet wire 200ft spool
l 1 - Miniature Incandescent Lamp, 1.5V 25mA
l 1 - Cardboard strip, 8cm x 30cm
l 1 - Large nail, 8cm long or more
l Misc. - Knife or sandpaper to strip the wires
l Misc. - tape to hold wire down
l Optional: hand drill or electric drill to spin it
(hand drill is best)
CONSTRUC
First make
the hollow-ended box. Score the cardboard
TION
strip like so:
Fold it like this and tape it securely.
Use the nail to poke a hole perfectly straight through the

center of the box, going through both sides and all (hole)
three layers of cardboard. Then pull the nail out and use
it to widen all the holes slightly, so when you put the nail
back through, it will be a bit loose and able to spin.
At this point you should clamp four magnets around the

nail and giveit a spin. This makes sure the box is large
enough. The nail andmagnets should spin freely. The
corners of the magnets should NOT bump the inside of
the box as they spin. If the box is a bit too small, start
over and make it a little bigger. Either that, or try a
thinner nail.
Pick the spool of number-30 magnet wire From the kit of
spools. This is the thinnest.Tape one end of the number-
30 magnet wire to the side of the box, then wind all of

the wire onto the box as shown. It's OK to cover up the
nail hole.
Pull the taped end of the wire out, then tape down both
of the wires so the coil doesn't unwind.
You should have about 10cm of wire left sticking out.Use
sandpaper or the edge of a knife to scrape the thin
plastic coating off 2cm of the wire ends.Remove every bit
of red coating, so the wire ends are coppery.
Spread the wire away from thenail hole and tape it in
place.Stick the nail back through the holes and make
sure it can spin.
Take your four magnets, stick them face to face in two
pairs, Then stick the two pairs inside the box and on
either side of the nail so they grab the nail. Push them
around until they are somewhat balanced and even, then
spin the nail and see if they turn freely. If you wish, you
can stick 2cm squares of cardboard
between the magnets to straighten them, and tape the

magnets so they don't move around on the nail
Make sure that each end of the generator's wires are
totally cleared of red plastic coating. If there is a bit of
plastic left, it can act as an insulator which turns off your
light bulb circuit.
Twist the scraped end of each generator wire securely
around the silver tip of each wire from the small light
bulb.
(If necessary, use a knife to strip more plastic from the
ends of the light bulb wires.) One generator wire goes to
one light bulb wire, the other generator wire goes to the
other light bulb wire, and the two twisted wire
connections should not touch together. In the twisted
wires, metal must touch metal with no
plastic in between.
WORKI
NG
All metals contain a movable substance called "electric
charge". Even uncharged wires are full of charge! After
all, the atoms of the metal are made half of positive
protons and half of negative electrons. Metals are special
because their electrons don't stay connected to the
metal atoms, instead they fly around inside the metal
and form a type of electric "liquid" inside the wires. All
wires are full of electric fluid. Modern scientists call this
the "electron sea" or "electron gas." It is not invisible, it
actually gives metals their silvery shine. The electron gas
is like a silvery fluid.
When a circle of wire surrounds a magnetic field, and the
magnetic field then changes, a circular "pressure" called
Voltage appears. This circular voltage trys to force the
movable charges in the wire to rotate around the circle.
In other words, moving magnets create electric currents
in closed circles of wire. A moving magnet causes a
pumping action. If the circuit is not complete, if there is a
break, then the pumping force will cause no charge flow.
But if the circuit is "complete" or "closed", then the
magnet's pumping action can force the electrons of the
coil to begin flowing. This is a basic law of physics, and it
is used by all coil/magnet electric generators.
When the circuit is closed and the magnet is moving,

charges in the metal are forced to flow. The charges of
the light bulb's filament are pushed along. When the
charges within the copper wire pass into the thin light
bulb filament, their speed greatly increases. When the
charges leave the filament and move back into the
US
1. Aircraft auxiliary power generation, wind
ES
generators,
high speed gas turbine generators.
2. Hybrid electric vehicle (HEV) drive systems,
automotive starter generators.
3. An ac generator, or 'alternator', is used to
produce ac voltages for transmission via the grid
system or, locally, as portable generators.
4. All of our household appliances runs on ac
current.
Ex: Refrigerator, washing machines, oven, lights,
fan etc.
EFFICIE
NCY
Expression
for Instantaneous e.m.f. Produced:
Let position of the coil at any time t. It make angle q with
vertical. If w is uniform angular speed of the coil.
Then q = wt
B be the strength of magnetic field n be the number of

turns in the coil and A area of the coil then magnetic flux
with the coil in this position is given by:
f = nBA Cos q = nBA Cos wt.
Differentiate w.r.t. time

= nBA (-Sin wt) w
= -nBA w Sin wt
e = - (-nBA w Sin wt)
maximum value of e.m.f. say E0
e = E0 Sin wt
1)Efficiency of an AC generator is the ratio of the useful
power output to the total power input.
2)Because any mechanical process experiences some
losses, no AC generators can be 100 percent
efficient.
3)Efficiency of an AC generator can be calculated using

Equation.
4)Efficiency =(Output /Input )x 100
BIBLIOGRA
PHY
1)NCERT
textbook class 12
2) INTERNET
3) www.yahoo.com
4) www.scribd.com
5) www.google.com
KENDRIYA VIDYALAYA
BALASORE
DEPARTMENT OF PHYSICS
CERTIFICATE
This is to certify that BIJAYA LAKSHMI, a student

of class XII-A has successfully completed the
research on the below mentioned project under the
guidance of MS. SASMITA GIRI ( Subject Teacher )
during the year 2015-16 in partial fulfillment of
physics practical examination conducted by
AISSCE, New Delhi.
Signature of external examiner Signature of

physics teacher

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ACKNOWLEDGEMENT

In the accomplishment of this project successfully, many

Primarily I would thank god for being able to complete

Then I would like to thank my parents and friends who

been helpful in various phases of the completion of the

energy. A generator forces electric current to

hand crank, compressed

provide nearly all of the power for electric

Fold it like this and tape it securely.

Use the nail to poke a hole perfectly straight through the

At this point you should clamp four magnets around the

30 magnet wire to the side of the box, then wind all of

between the magnets to straighten them, and tape the

When the circuit is closed and the magnet is moving,

B be the strength of magnetic field n be the number of

f = nBA Cos q = nBA Cos wt.

Differentiate w.r.t. time

e = - (-nBA w Sin wt)

maximum value of e.m.f. say E0

3)Efficiency of an AC generator can be calculated using

This is to certify that BIJAYA LAKSHMI, a student

Signature of external examiner Signature of

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