# Investigatory Project in Physics for Class 11

INVESTIGATORY PROJECT – 1

THE DEVIATION FROM OHM'S LAW

Aim: To study the deviation from ohm's law due to the change of temperature of the conductor.

Materials and apparatus

(i) A resistance wire (of resistance about 1 Ω) connected between two terminals which are fixed on a wooden strip.

(ii) Sensitive ammeter of range about 3A

(iii) Digital voltmeter

(iv) Rheostat

(v) Battery eliminator

(iv) Key etc

Procedure

Connections are made as shown in the figure. The current I and p.d across the resistance R are measured. V/I is calculated. Sufficient current is sent through the resistor by adjusting the rheostat so that it is heated. V/I is calculated. The experiment is repeated for different values of current. It is seen that V/I is not a constant and it increases with the increase in current.

INVESTIGATORY PROJECT – 2

THE SELF INDUCTION

Aim: This is a project to study the process of self induction.

Material required

(i) 6V torch bulb

(ii) 3-0-3, 500 mA transformer

(iii) A piece of PVC pipe

(iv) A wooden plank or card board piece

(v) Connecting wire

(vi) 22 gauge finely insulated copper wire about 100 gram

(vii) iron pieces

Procedure

Fix the transformer on the wooden plank. Connect the wires from the output of the transformer to the bulb. The middle wire should not be used. Wind about 450 turns of the copper wire on the PVC pipe and fit it on the board. The end B of the solenoid is connected to the bulb. Connect wires from P to C and from R to B. Apply 230 V ac mains to transformer. The voltage gets stepped down to 6V. The bulb glows. Disconnect the wire from R to B and connect it to the point A. The bulb will become dim. The ac when passed through the solenoid creates changing flux which induces the back end. Then the bulb becomes dim. If soft iron bars are introduced into the PVC pipe, the back emf increases due to increased flux density. Hence the effective voltage decreases and the bulb will become dimmer.

INVESTIGATORY PROJECT – 3

THE ELECTROMAGNETIC INDUCTION

Aim: This is a project meant to study electromagnetic induction.

Materials needed

(1) Finely insulated copper wire of gauge 24 about 100 gram

(ii) A piece of GI pipe

(iii) Magnet from a loud speaker

(iv) Two LEDs preferably of different colours.

Procedure

Wind about 450 turns of copper wire on the GI pipe and attach the two LEDs at the ends of the wire in such a way that they are in opposite directions. Move a magnet to and fro inside (or near) the coil very quickly. The coil will experience a change of flux. Hence an emf will be induced and current will flow. The LED will glow indicating the presence of current. When the magnet moves upward one LED will glow but when the magnet is made to move in the downward direction, the other LED will glow. This indicates that the current is reversing direction i.e., it is AC.

INVESTIGATORY PROJECT – 4

The IMPROVISED RESONANCE COLUMN

Aim: This project is meant to show resonance and to calculate the velocity of sound in air.

Materials needed

(i) A fused tube light

(ii) Tube of a cycle tyre

(iii) A stand

(iv) A tuning fork and a rubber hammer

Procedure

Both the ends of a fused tube light are carefully cut open. The inside surface of the tube is washed to remove the coating. Thus we get a tall glass tube for the resonance column. The glass tube is clamped vertically on a stand. A long cycle tube with both ends open is taken. One end of the tube is slipped on to the lower end of the glass tube. The other end of the rubber tube is closed by tying the end with a thread. The rubber tube is rolled up.

The glass tube is filled with water. An excited tuning fork of frequency f is kept horizontally over the mouth of the glass tube. The rubber tube is slowly unrolled so that the water level in the glass tube is slowly lowered and length of the air column inside the tube gradually increased till a booming sound is heard. Now the air column vibrates in resonance with the tuning fork. The length l of the air column is measured. The velocity v of sound at room temperature is calculated using the equation,

V = 4lf

INVESTIGATORY PROJECT – 5

THE BIASING OF A TRANSISTOR

You all know that the transistor is known as wonder child of electronics. This is a project to realize that a transistor work only when its emitter junction is forward biased and collector junction is reverse biased.

Materials needed

(i) A one kΩ resistor

(ii) A transistor - AD 149

(iii) A 6V bulb

(iv) Connectng wires

(v) 1.5 V torch cell

Procedure

Connect the resistor, transistor and bulb as shown in the figure. The transistor is PNP. Now apply 1.5 volt dc with positive at A and negative at B. The bulb glows. Now the emitter junction is forward biased and collector junction is reverse biased. Hence the transistor conducts. If the voltage is reversed the emitter junction will be reverse biased. Hence the transistor will not conduct. The bulb will not glow.

INVESTIGATORY PROJECT – 6

THE PULSE AMPLIFIER

Aim: This is a project meant to show the amplification.

Materials required

(i) Transistors BC 548, BC 558

(ii) LED

(iii) 100Ω resistor

Procedure

Arrange the devices as shown in the circuit. Our body has a small voltage. At the point A you touch with the finger. The body voltage is applied at the base. In the first transistor this voltage gets amplified and the output goes as input of the second transistor. Reamplification takes place. Output makes the LED glow. When we take off the hand from the base the whole process stops.

When the base of the first transistor BC 548 is touched the body voltage makes the base emitter junction forward biased. The transistor conducts and its amplified output is fed as the input of the second transistor BC 558. The second transistor amplifies its input and the amplified output makes the LED glow.