Physics Project File for Class 12th.

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Object Demonstration of induced current in a coil as bar magnet is moved inside the coil.

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Principle 1.Whenever magnetic S flux linked with coil Bar Magnet be changed the e.m.f. N is induced in coil. 2.Induced e.m.f. is directly proportional G to rate of change of Clamp Coil of magnetic flux. about 250 turns 3.Direction of induced Wooden Stand current always A bar magnet moved in oppose the cause by & out of a coil produces which induced current in the it is produced. coil in both the cases. The galvanometer shows deflection. vAIBHAv

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Observation • When a bar magnet is placed near the coil no deflection is observed in galvanometer.

S N rapidly towards the G • When North pole of magnet is moved coil, the galvanometer shows deflection. When magnet is stopped the deflection in galvanometer becomes zero. When speed of magnet is increased the deflection is increased.

S N

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G

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• When North pole of magnet is taken away from the coil rapidly, the galvanometer shows deflection but in opposite direction. When magnet is stopped the deflection in galvanometer becomes zero. When speed of magnet is increased the deflection is increased. S N G

• When Southpole of magnet faces the coil & the magnet is moved towards or away from the coil, the galvanometer again shows deflection but in opposite direction. S

N S

N G

G

• When magnet is kept stationary & coil is moved towards or away from magnet, then there is a deflection in the galvanometer. vAIBHAv

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Explanation When there is no relative motion between the magnet & the coil, the magnetic lines of force passing through the coil is definite i.e. the magnetic flux linked with coil is constant. When there is relative motion between the magnet & coil & magnet is moved towards the coil the magnetic lines passing through coil increases. When magnet moves away magnetic field lines passing through coil decreases. According to Faraday Laws e.m.f. induced when magnetic flux linked with coil be changed. When magnetic flux linked with coil increases then galvanometer shows deflection in one direction when it decreases it shows deflection in opposite direction. vAIBHAv

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Conclusion • Whenever there is change in Magnetic Flux linked with the coil current is induced in coil. • Direction of induced current always opposes the cause by which it is produced.

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Object Demonstration of working of light dependent resistor using simple circuit like automatic car parking light / automatic switches. vAIBHAv

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Principle The light dependent resistor is a resistor whose resistance value depends upon the intensity of light falling on it. LDR resistance decreases with increasing light level.

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Circuit Diagram & Component Used Components : 1.A transistor(n-pn) 2.A LED 3.Battery 4.Resistor 10kΩ, 1kΩ 5.Light Dependent

R

10kΩ

1kΩ

6V 0.06A BC 108 or ZTX 300

6V

ORP 12

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Observations • When light falls on the LDR the LED will not glow. • When light doesn’t fall on the LDR the LED will glow.

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Explanation • Construction Of LDR :It is made up of high resistance semiconductor. The light sensitive part of the LDR is a wavy track of cadmium sulphide. CdS cells rely on the materials ability to vary its resistance according to the amount of light striking the cell. Cadmium sulphide track

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• Working : • If the light falling on the devices is of high enough frequency, Photons absorbed by the semiconductor give bound electorns enough energy to jump into conduction band. The resulting free electron conduct electricity, thereby lowering V = resistance. 9V R 10 • Suppose the LDR has a resistance of . kΩ 5kΩ in bright light & 200kΩ in the V shade LDR in

top

out

Lowin the

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When the LDR is in the light Vout will be Vout Rbottom

Vout V

=

Rbottom

+ Rtop

=

0.5

x 9

=

0.43

x 9

=

8.57

0.5 + 10 In the shade Vout will be Vout V

=

200 200 + 10

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Conclusion • This circuit gives a low voltage when the LDR is in the light & a high voltage when the LDR is in the Shade.

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