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BAPATLA ENGINEERING

COLLEGE::BAPATLA

(AUTONOMOUS)

Department of Physics

Laboratory Manual

Engineering Physics

PHL 101 & PHL201

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B.TECH PHYSICS LAB MANUAL

CYCLE-1

1. COMPOUND PENDULUM

2. MAGNETIC FIELD ALONG THE AXIS OF A CURRENT CARRYING CIRCULAR COIL.

3. NEWTON RINGS

4. SOLAR CELL

5. DETERMINATION OF ENERGY GAP OF A SEMICONDUCTOR

CYCLE-2

6. HALL EFFECT

7. RESONANCE IN L-C-R CIRCUIT

8. DIFFRACTION GRATING

9. CHARACTESTICS OF A PHOTO CELL

10.DETERMINATION OF WAVELENGTH OF LASER LIGHT BY

DIFFRACTION GRATING

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Name of the student____________________ Branch & Roll No

LIST OF EXPERIMENTS

INDEX

S.No Name of the experiment Page numbers

1 Compound pendulum 1- 3

2 Torsional pendulum 4-5

3 Sonometer 6-7

4 Newton rings 8-9

5 Diffraction Grating 10-11

6 Air wedge 12-13

7 Dispersive power of a prism 14-16

8 Wavelength of LASER diode 17

9 Photo cell 18-19

10 Solar cell 20-21

11 Field along the axis of a circular coil 22-23

12 Platinum resistance thermometer 24-26

13 Forbidden energy gap of semiconductor 27-29

14 Hall effect 30-32

15 Cathode ray oscilloscope 33-34

16 Resonance in LCR circuit 35-36

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COMPOUND PENDULUM

AIM :To determine acceleration due to gravity ( g )at a place using compound pendulum.

APPARATUS: Compound pendulum, knife edges, telescope, stop watch, meter scale.

DEFINATION OF g : When a body is left to free fall, then it acquires a constant acceleration andmove to a ds ea th, due to ea th s g a itatio . No the o sta t a ele atio a ui ed that f eel falli g od is called acceleration due to gravity.

FORMULA: Time period of oscillation of a physical pendulum or compound pendulum is given by

= + Compare the above formula with time period of oscillation of a simple pendulum. i.e. = Here = + is alled le gth of e ui ale t si ple pe dulu . K is adius of g atio ; D is dista e of the poi t of suspe sio f o e te of g a it . The alue of L is esti ated f o a g aph d a et ee distance of point of suspension ( ) verses time period of oscillation (T)

From the above formula acceleration due to gravity is given by = cm/s2 THEORY:

In lower classes you might be familiar with simple pendulum experiment for the determination of

acceleration due to gravity, hence before to do this experiment one has to know the difference between

simple pendulum, and compound pendulum experiment, oth of the e e ea t fo dete i atio of g value. They are

1. Simple pendulum is an ideal case, because it require a point mass object

2. It requires torsion less string.

The above mentioned two conditions are not practically possible, hence it is only a mathematical ideal case,

and whereas compound pendulum is a physical pendulum.

A rigid body of any shape which is free to oscillate without any friction on a vertical plane is called

compound pendulum. It swings harmonically back and forth about a verticalz-axis (Passing through

point O as sho i Fig , he o pou d pe dulu is displaced from its equilibrium position by an angle . In the equilibrium position, the center of gravity of the body is vertically below at a distance of OG. Let the mass of the body is m, In this experiment you are going to measure theacceleration

due to gravity, g by observing the motion of a compound pendulum. Let us consider acompound

pendulum shown in figure 1.

Pull the compound pendulum through an angle and release it, then it makes angular oscillations due

totorque acting on it, given by

= = = Here ve sign is because of force and displacement is opposite to each other. For small amplitudes Now expression (1) becomes = We know that torque = [ ]

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= => = + ( ) =

Here is the o e t of i e tia of pe dulu , a out a a is passi g th ough poi t O . Equation (2) represents simple harmonic equation of the form, i.e. + = Here is angular frequency of simple pendulum. From comparison with Eq (2), we can write = => = = => = According to parallel axes theorem, the rotational moment of inertia, about any axis parallel to the one

passing the center of gravity is given by = + We k o that o e t of i e tia a out a a is passi g th ough e te of g a it G , gi e = He e K is adius of g atio of the od a out a a is passi g th ough G .

Thus = + = + Comparing expression (5) with expression for time period of simple pendulum i.e. = This suggests that = + = + = The term L is called length of equivale t si ple pe dulu . This is e ause si ple pe dulu of le gth L is ha i g a ti e pe iod, sa e as that of ti e pe iod of compound pendulum. Also it seems that all the mass of the body were concentrated at point , along

OG p odu ed su h that = + = + The poi t is alled e te of os illatio . I a alog ith si ple pe dulu e a suppose that, the entire mass is concentrated at that point.

From expression (6), the extra distance = is elo the e te of g a it G , at a poi t , a d is shown in Figure (1).

From expression (6) we can write + = The above equation is a quadratic equation i D a d it s t o oots a e gi e = + = That is for each half of pendulum, there are two different points of oscillation (do not get confusion with

center of oscillation) i.e. which are at distance away from center of gravity G , for which the value of L is same. Since L is same for , then, the time period is also same. When we perform this e pe i e t o oth sides of e te of g a it G e ha e a total of poi ts poi ts o o e side ha i g sa e ti e pe iod T , as sho i Figu e . The points are clearly shown in Graph.

It is so eti es o e ie t to spe if , the lo atio of a is of suspe sio o poi t of os illatio O , the dista e f o e d of the a , i stead of dista e D f o e te of g a it . B a i g the position of axis of suspension, measure the corresponding time period, and tabulate all the observation in the following

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TABULAR FORM FOR THE DETERMINATION OF TIME PERIOD

S.No

Distance of knife edge

from one end of the bar.

D

Time taken for 20 oscillations Time period

T=t/20 Sec

Trail 1 Trail 2 Mean time

( t ) sec

1

2

TABULAR FORM FOR THE DETERMINATION OF EQUIVALENT LENGTH OF SIMPLE PENDULUM

S.No Ti e period T T2 AC BD = + = 1

2

Graph:

1. D a a g aph et ee D alues o -a is a d o espo di g T alues o Y- axis, then we get the follo i g atu e of g aph. Fig . D a a st aight li e, at o e pa ti ula T alue, the it i te se t the graph at four points and mark them as A,B,C,& D

Fig. T erses D graph for ea h half of the o pou d pe dulu GRAPH 2.

A g aph is d a et ee L alues o X-a is a d o espo di g T2 alues f o ta le , o Y-axis, and then the nature of graph is as shown in Fig4

NOTE: We a also fi d L alue f o Fig as su of . We can show it assum of expression for & . i.e. L=D1 + D2 = PA + PB (According to Fig1) + = + + = = PRECAUTIONS: 1.Angular displacement of the pendulum should be confined to below 10

o

2. Pendulum should oscillate only in vertical plane, without wobbling.

3. Knife edge should rest on horizontal surface only.

RESULT:Acceleration due to gravity using compound pendulum was found to be ______.

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TORSIONAL PENDULUM-- RIGIDITY MODULUS

AIM: To determine the rigidity modulus of the material of the wire by the method of oscillations.

APPARATUS: Circular disc with chuck, given wire (suspension wire), stop clock, two equal

cylindrical masses, screw gauge, vernier calipers and meter scale.

FORMULA: Rigidity modulus of given wire using torsional pendulum is given by = / Here m=mass of each cylinder

= length of the wire

a = radius of the wire & & & THEORY:

Torsion pendulum consists of a metal wire clamped to a