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Demonstration of induced current in a coil as bar magnet is moved

inside the coil.

Object

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Principle

S

NBar Magnet

G ClampCoil of about 250 turns

Wooden Stand

1.Whenever magnetic flux linked with coil be changed the e.m.f. is induced in coil.

2.Induced e.m.f. is directly proportional to rate of change of magnetic flux.

3.Direction of induced current always oppose the cause by which it is produced.

A bar magnet moved in & out of a coil produces induced current in the coil in both the cases. The galvanometer shows deflection.

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Observation• When a bar magnet is placed near the coil no

deflection is observed in galvanometer.

• When North pole of magnet is moved rapidly towards the 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

S N

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.

• 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.

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

S N

S NN S

GG

G

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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.

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

Object

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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

R 10kΩ

1kΩ

ORP 12

6V0.06A

BC 108 or ZTX 300

6V

Components : -

1.A transistor(n-p-n)2.A LED3.Battery4.Resistor 10kΩ, 1kΩ5.Light Dependent Resistor

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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 resistance.

• Suppose the LDR has a resistance of .5kΩ in bright light & 200kΩ in the shade Vout

Low in

the light

Vin = 9V

LDR

Rtop 10 kΩ

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When the LDR is in the light Vout will be

Vout = Rbottom

Rbottom + Rtop

Vout = 0.5 x 9 = 0.43 V

0.5 + 10

In the shade Vout will be

Vout = 200 x 9 = 8.57 V

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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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