engineering physics lab manual

47
Malla Reddy Engineering College for Women Engineering Physics Lab [1] Instructions for Laboratory The objective of the laboratory is skill development. The experiments are designed to illustrate phenomena in different areas of Physics and to expose you to measuring instruments. Conduct the experiments with interest and an attitude of learning. Students are expected to be well prepared for the experiment when they come to the lab. Work quietly and carefully (the whole purpose of experimentation is to make reliable measurements!) and equally share the work with your partners. Be honest in recording and representing your data. Never make up readings or doctor them to get a better fit for a graph. If a particular reading appears wrong repeat the measurement carefully. In any event all the data recorded in the tables have to be faithfully displayed on the graph. All presentations of data, tables and graphs calculations should be neatly and carefully done. Bring necessary graph papers for each of experiment. Learn to optimize on usage of graph papers. Graphs should be neatly drawn with pencil. Always label graphs and the axes and display units. If you finish early, spend the remaining time to complete the calculations and drawing graphs. Come equipped with calculator, scales, pencils etc. Do not fiddle idly with apparatus. Handle instruments with care. Report any breakage or damage to the Instructor. Return all the equipment you have signed out for the purpose of your experiment.

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Page 1: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[1]

Instructions for Laboratory

The objective of the laboratory is skill development. The experiments are designed to

illustrate phenomena in different areas of Physics and to expose you to measuring

instruments. Conduct the experiments with interest and an attitude of learning.

Students are expected to be well prepared for the experiment when they come to the

lab.

Work quietly and carefully (the whole purpose of experimentation is to make reliable

measurements!) and equally share the work with your partners.

Be honest in recording and representing your data. Never make up readings or doctor

them to get a better fit for a graph. If a particular reading appears wrong repeat the

measurement carefully. In any event all the data recorded in the tables have to be

faithfully displayed on the graph.

All presentations of data, tables and graphs calculations should be neatly and

carefully done.

Bring necessary graph papers for each of experiment. Learn to optimize on usage of

graph papers.

Graphs should be neatly drawn with pencil. Always label graphs and the axes and

display units.

If you finish early, spend the remaining time to complete the calculations and drawing

graphs. Come equipped with calculator, scales, pencils etc.

Do not fiddle idly with apparatus. Handle instruments with care. Report any breakage

or damage to the Instructor. Return all the equipment you have signed out for the

purpose of your experiment.

Page 2: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[2]

EXPERIMENT 1

DISPERSIVE POWER OF THE MATERIAL OF THE PRISM

SPECTROMETER

AIM:

To determine the dispersive power of the material of the given prism

APPARATUS:

Spectrometer, Mercury vapor lamp, crown glass prism, reading lens, spirit level and

reading lamp

THEORY:

The Refractive index ‘µ’ of the material of the prism is given by 2

2

A DSin

ASin

--- (1)

Where ‘A’ is the Angle of the prism and ‘D’ is the angle of minimum deviation.

The Dispersive power ‘ω’ of the material of prism is given by 1

RB --- (2).

Where ‘μB ‘ is the Refractive index of the Blue line and ‘μR ‘ is the Refractive index of the

Red line. The quantity ‘µ’ is given by the equation 2

RB

---------- (3)

Where

sin2

sin2

B

B

A D

A

and

sin2

sin2

R

R

A D

A

. In this equation DB and DR are the

angle of minimum deviation for blue and red lines respectively. This can be calculated from

the spectrometer reading by taking the difference between the direct reading and reading

corresponding to each line.

1 1 2 2( ) ( )

2B

DV BV DV BVD

and 1 1 2 2( ) ( )

2R

DV RV DV RVD

Page 3: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[3]

PROCEDURE:

Preliminary adjustments on the telescope and

collimator

Focusing of the telescope – to get parallel

rays. The telescope has to be pointed towards a

distant object and adjusting the rack and pinion

arrangement a clear image has to be viewed

without parallax error. Make sure that cross wire is

clearly visible. The arrangement should not be

disturbed until the end of the experiment.

Adjustment on the collimator – to get parallel rays. Collimator and telescope are kept in

line with light source. The collimator slit width has to be adjusted to minimum. Looking

through the telescope rack and pinion arrangement on the collimator is adjusted to get a clear

bright and distinguished image of the slit without parallax error. This arrangement also

should not be disturbed until the end of the experiment.

Vernier table and prism table have to be leveled using spirit level. There are two verniers

are on the vernier table. Adjust one of the vernier zero to coincide with main scale zero.

Taking the readings on the vernier scales. Vernier table consist of a circular scale of

reading 0 to 360 degree. Each degree is divided into two and each half is equal to 30 minute.

Vernier scale has 30 divisions ( 31 lines) marked from 0 to 30. The reading comes just before

the vernier zero or exactly coinciding with the vernier zero is the main scale reading. If the

vernier zero does not coincide with any of the main scale divisions we have to look for

vernier scale divisions. Starting from the first vernier line see that if any venier line is exactly

coinciding with any of the main scale divisions. The venier scale division which appears to

be in coincidence with any one of the main scale division is the vernier scale position. Count

from vernier zero to that line and this number is the vernier reading. Repeat the same for

second vernier scale.

Direct reading - The prism is placed on the prism table with one of the transparent

faces facing the collimator and the other towards the telescope. The cross wire of the

Page 4: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[4]

telescope is brought in coincidence with the narrow slit and the telescope is fixed there.

Reading corresponding to this is noted on the Vernier I and Vernier II. This is the direct

reading

Minimum deviation position - The telescope is brought towards the base of the prism

and diffracted beam of light ( VIBGYOR spectrum ) is viewed. Looking at the spectrum

through the telescope (focus on one color line) the prism table is slowly rotated on to one

side. The deviated ray also moves on to the same side for some time and then the ray starts

turning back even though the prism table is rotated in the same direction. The point at which

the ray starts turning back is called minimum deviation position. In this limiting position of

the spectrum, deviation of the beam is minimum.

The cross wire of the telescope has to be fixed on the blue color and the reading is

noted on the Vernier I and Vernier II and tabulated. The same has to be repeated for red color

also. These are the readings of the minimum deviation position for blue and red rays.

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Malla Reddy Engineering College for Women Engineering Physics Lab

[5]

Fig: 2 Arrangement of prism for dispersive power

The difference between the direct reading and the deviated reading gives the angle of

minimum deviation for each color. Assuming the angle of prism as 600, the refractive index

for each color can be determined from eqn (1). Hence the dispersive power of the material of

the prism can be determined by using the eqn (2).

OBSERVATION

TABLE 1 Spectrometer reading

Angle of the Prism A =

Least count =( value of one MSD)/( no of divisions on the vernier scale)= ---------

= ---------- min

S. No. MSR

(a) VSD

VSD x L.C

(b)

Total

(a + b)

Blue V1

V2

Green V1

V2

Direct

Reading

V1

V2

CALCULATIONS

PRECAUTIONS:

1. The surrounding should be perfectly dark.

2. The prism table should be leveled by using spirit level.

3. After making the preliminary adjustments the collimator should not be disturbed.

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Malla Reddy Engineering College for Women Engineering Physics Lab

[6]

RESULT:

The Dispersive power of the material of the prism is determined and its value is _________.

VIVA QUESTIONS:

1. What is meant by monochromatic light?

2. What is meant by dispersion?

3. What is minimum deviation?

4. When light rays travel through a prism what happens?

5. What is the use of collimator?

6. What are the advantages of keeping the prism in minimum deviation position?

7. What are the different colors in white light?

8. What is the role of telescope?

Page 7: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[7]

EXPERIMENT 2

RIGIDITY MODULUS OF A WIRE - TORSIONAL PENDULUM

AIM:

To determine the rigidity modulus of the material of the given wire by Torsional

pendulum

APPARATUS:

Torsional pendulum, wire, stop watch, meter scale, screw gauge and Vernier calipers

THEORY:

When the disc is turned through a small angle in horizontal plane and then released, it

makes torsional oscillations about the axis of the wire. The period of oscillation is given by

C

IT 2 ----------------------- (1)

Where 2

2

RI M the moment of inertia of the disc about the axis of rotation and C=couple

per unit twist of the wire. If ‘a’ is the radius of wire ‘l’ is the length of the wire between

chucks and ‘η’ is the rigidity modulus of the material of the wire, then the couple ‘C’ per

unit twist of the wire is given by l

aC

2

4 ------------------ (2)

From (1) & (2), we get

24

8

T

l

a

I -------------- (3)

On substituting the values of ‘MI’ ( moment of inertia) in equation (3), we get

24

24

T

l

a

MR Dyne /cm

2

Where η =Rigidity modulus of the wire, M= Mass of the disk ( gm)

R = radius of the disc (cm), a = radius of the wire (cm), l = length between the chucks (cm)

T = Time taken for one oscillation (sec)

Page 8: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[8]

PROCEDURE:

Torsional pendulum consists of a uniform metal disc suspended by a wire whose

rigidity modulus is to be determined. The lower end of a wire is gripped in a chuck fixed at

the center of the disc and the upper end is gripped in another chuck fixed to wall bracket

A torsional pendulum of length l = 80 cm is

set up. The metallic disc is turned through a small

angle about the axis passing through the center and

normal to the plane of the disc and then swiftly

released. The disc starts making torsional

oscillations. Care should be taken while releasing the

disc from the turned position so that it should not get

wobbling or linear oscillations. Using a stop watch

measure the time taken for twenty oscillations. If

you consider the reference line, one complete

oscillation means mark on the disc starting from the

reference line and then come back to the point again. Without disturbing the oscillating

pendulum measure the time taken for twenty oscillations for a second time. If both trials are

giving comparable result, readings can be recoded on the observation. The same procedure

has to be repeated for pendulums of different length. On dividing the time taken for 20

oscillations by 20 we get the period of oscillation. A graph is plotted with ‘l’ on the y axis

and T2 on the x axis. Slope of the graph is calculated and used in the equation for calculating

rigidity modulus.

Diameter of the disc is measured using a vrnier scale and divided by two to get its radius.

Diameter of the wire is measured using a screw gauge

and divided by two to get its radius.

GRAPH:

A graph is drawn taking the value of ‘l’ on Y-axis and T2

on X axis. It is straight line passing through origin.

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Malla Reddy Engineering College for Women Engineering Physics Lab

[9]

OBSERVATIONS

Mass of the disc (m) = gm.

Average radius of the disc (R) = cm

Average radius of the wire (a) = cm.

TABLE: PERIOD OF OSCILLATION

S. No Length of wire

between chucks

‘l’ cm

Time for 20 oscillations (sec) Time period

T= x / 20

sec

2T

l

cm/sec2

Trial 1 Trial 2 Mean

‘x’

VERINER SCALE READING DIAMETER OF THE DISC

Least count = value of one main scale division / no of vernier scale divisions =

S. No M.S.R

‘a’ cm VSD

VSD X L.C

‘b’ cm

Total

(a+b)cm

Page 10: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[10]

Radius of the disc =( mean diameter /2) = cm

Screw gauge reading diameter of wire

Pitch of the screw = distance moved on the pitch scale/ no of rotations on the head scale

= mm

Least Count of Screw gauge= divisionsscaleheadofno

screwtheofPitch

.

= mm

Zero reading = Zero Correction =

S. No P.S.R

‘a’mm

Head scale reading C.H.S.R X

L.C

‘b’ mm

Total

(a+b) mm observed Corrected

RESULT: The rigidity Modulus of the material of a given wire is -----------

PRECAUTIONS:

1. The wire should be free from kinks.

2. The disc shouldn’t wobble.

3. The amplitude of the disc must be small.

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Malla Reddy Engineering College for Women Engineering Physics Lab

[11]

VIVA QUESTIONS:

1. What is stress?

2. What is strain?

3. What is hook’s law?

4. What is rigidity modulus?

5. What is Young’s modulus?

6. What is bulk modulus?

7. What are Transverse waves?

8. What are longitudinal waves?

9. What is one oscillation?

10. Explain elastic limit?

11. What are the different elastic moduli explain all?

Page 12: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[12]

EXPERIMENT 3

MELDE’S EXPERIMENT – TRANSVERSE AND LONGITUDINAL

MODES

AIM

To determine the frequency of the given tuning fork using Melde’s arrangement.

APPARATUS

Melde’s apparatus (electrically driven tuning fork, thread, a small pan, smooth

frictionless pulley fixed to stand) weight box, meter scale, a battery eliminator and

connecting wires.

THEORY

When the tuning fork vibrates, the vibrations travels along the thread as waves and

gets reflected back at the pulley. The forward and reflected waves superimpose on the thread

and standing waves are created. This makes loops on the thread. By adjusting the weight in

the pan the loops can be made well defined.

Transverse arrangement – In this arrangement the prongs of the tuning fork vibrate in

a direction normal to the length of the thread. In this case frequency of the thread and tuning

fork will be same and it is given by the equation 1

2

T

l

Longitudinal arrangement – In this arrangement prongs of the tuning fork vibrate in a

direction along the length of the thread. In this case frequency of the thread is just half that of

the tuning fork and it is given by 1 T

l

l = length of one loop,

T = (M + m ) * g - tension acting on the thread,

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[13]

µ (linear density) = (mass of the thread)/( total length of the thread) = m/L

PROCEDURE:

Melde’s apparatus is an electrically vibrated tuning fork. In between the prongs of the tuning fork

an electromagnet is fixed. By the side of the electromagnet a circuit breaker arrangement is also

attached as in the case of an electric bell. Once the power reaches the magnet it attracts the prongs of

the tuning fork and as result electrical connection to the magnet will be lost and when the prongs

come to the normal position again the electrical connection established. The process continues and the

tuning fork starts vibrating.

LONGITUDINAL MODE The apparatus is arranged in the longitudinal position so that the prongs

vibrate parallel to the thread. The thread is made horizontal and length of the thread between the

pulley and the prong is adjusted to be one meter. The circuit is closed. Load in the pan is gradually

increased until clear and well-defined loops appear in the thread. Count the number of loops and note

down the weight placed in the pan. Increase gradually the weights in the pan until clear and well

defined loops appear again on the thread. Note down the weight in the pan and number of loops. As

the weight in the pan increases number of loops should decrease. Repeat the same for three or four

times.

TRANSVERSE MODE In the transverse mode the instrument has to be kept in the

transverse position and the same procedure described above has to be followed

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[14]

OBSERVATIONS

Table 1 transverse mode

S. No Load in the

pan(M)

gm

Tension

T=(M+ m)g

dyne

No. of

loops

(x)

Length of

each loop

(l) cm

m

T

ln

2

1 Hz

The frequency of the tuning fork (n) = _______ Hz.

Table 2 Longitudinal mode

S. No Load in the

pan

(M) gm

Tension

T=(M+ m1)g

Dyne

No. of loops

(x)

Length of

each loop

(l) cm Hz

Page 15: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[15]

The frequency of the fork (n) = ________ Hz.

PRECAUTIONS:

1. The loops must be well defined.

2. The plane of vibration of the thread must be vertical.

3. In counting the no of loops, the loops at the two extreme ends must not be

counted.

RESULT:

By using Melde’s arrangement, the frequency of tuning fork is determined and the

values in Transverse arrangement and longitudinal arrangements are ------ Hz & ------ Hz

VIVA QUESTIONS:

1. Define Stationary & Progressive waves?

2. What is meant by resonance?

3. What is a Transverse wave?

4. What is a longitudinal wave?

5. What is the role of magnet?

6. Differentiate b/w Anti-Node & Node?

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Malla Reddy Engineering College for Women Engineering Physics Lab

[16]

EXPERIMENT 4

DETERMINATION OF WAVELENGTH OF A SOURCE

DIFFRACTION GRATING

AIM:

To determine the wavelength of the given light source using diffraction grating with

minimum deviation method

APPARATUS:

Plane diffraction grating, spectrometer, Sodium vapor lamp, reading lens with lamp

THEORY

Wave length of the given source calculated by the equation

2sin2

D

Nn

A

0

Where, ‘λ’ is the wave length of the line for which ‘D’ is the angle of minimum deviation

N = (15000 / 2.54) is known as grating constant. It gives the number of lines per

centimeter. The order of diffraction ‘n’ = 1

Substituting the value of minimum deviation for each line in the above equation wave length

of each line can be calculated

PROCEDURE

Focusing of the telescope – to get parallel rays. The telescope has to be pointed towards a

distant object and adjusting the rack and pinion arrangement a clear image has to be viewed

without parallax error. Make sure that cross wire is clearly visible. The arrangement should

not be disturbed until the end of the experiment Adjustment on the collimator – to get

parallel rays. Collimator and telescope are kept in line with light source. The collimator slit

width is adjusted to be minimum. Looking through the telescope rack and pinion

arrangement on the collimator is adjusted to get a clear bright and distinguished image of the

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Malla Reddy Engineering College for Women Engineering Physics Lab

[17]

slit without parallax error. This arrangement also should not be disturbed until the end of the

experiment.

Diffraction grating is mounted on the grating

stand fixed to the prism table in such a way that its

plane surfaces are normal to the collimator and

telescope. See the clear and well defined direct image

through the telescope. Turn the telescope to both left

and right sides and see the first order diffracted

image. Turn the telescope to left or right side and

keep the cross wire on one line. Adjust the grating

table by gradually turning it to one side until it

reaches the minimum deviation position. Fix prism

table and bring the cross wire exactly on D1 line and

note down vernier one and two readings. Then bring

the cross wire on D2 line note down the readings.

Bring back the telescope to direct reading position

and get the cross wire on the direct image. Note down

the vernier readings.

OBSERVATIONS

TABULAR COLUMN Spectrometer reading

Least count = mangnitude of one main scale division / number of vernier scale divisions

= min

S. No. MSR

(a) V.C.

V.C. x L.C

(b)

Total

(a + b)

D1 line V1

V2

D2 line V1

V2

Direct

Reading

V1

V2

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Malla Reddy Engineering College for Women Engineering Physics Lab

[18]

CALCULATIONS

PRECAUTIONS:

1. The prism table is to be leveled with a spirit level

2. Readings should be taken without parallax error

3. Rack and pinion screws of both the collimator and telescope should not be

disturbed, once the preliminary adjustments are done.

4. Back lash error should be voided.

RESULT:

Wavelength of (D1) and (D2) lines of sodium light is determined with the help of

diffraction grating by using minimum deviation method and are ------------.

VIVA QUESTIONS:

1. What is a heterochromatic source?

2. What are different colors in white light?

3. What is diffraction?

4. What is a diffraction grating?

Page 19: ENGINEERING PHYSICS LAB MANUAL

Malla Reddy Engineering College for Women Engineering Physics Lab

[19]

EXPERIMENT 5

MAGNETIC FIELD ALONG THE AXIS OF A COIL

STEWART & GEE’S METHOD

AIM:

To determine the magnetic induction at the center and at several points on the axis of

a circular coil carrying current using Stewart & Gee type of tangent galvanometer.

APPARATUS:

Stewart & Gee type of tangent galvanometer, Battery eliminator, Ammeter,

Commutator, Rheostat, plug key, scale, and connecting wires.

THEORY:

When a current of ‘I’ amps flows through a circular coil of ‘n’ -turns, each of radius

‘a’ units, the magnetic induction ‘B’ at any point P on the axis at a distance ‘x’ from the

center of the coil is given by

2/322

2

0

)(2 ax

niaB

Where x is the distance of the point P from the center of the coil

When the plane of the coil is placed parallel to the magnetic meridian, the direction of

the magnetic field of the coil will be perpendicular to the direction of the horizontal

component of the earth’s magnetic field say BH. The magnetic needle deflection

magnetometer placed at any point on the axial line of the coil, is acted up on by two magnetic

fields B & BH which are at right angles to each other. Therefore the needle deflects obeying

tangents law, B = BHTanθ

BH = 30.23µ0 newtons/amp.mts is the horizontal component of the earth’s magnetic field is

taken from the standard tables. The intensity of the field at any point is calculated from the

above equation and verified using the first equation.

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Malla Reddy Engineering College for Women Engineering Physics Lab

[20]

CIRCUIT DIAGRAM:

R – Rheostat, E – Battery, A – Ammeter

MODEL GRAPH:

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Malla Reddy Engineering College for Women Engineering Physics Lab

[21]

PROCEDURE:

Stewart & Gee apparatus consists of a coil of thick insulated wire of 5 to 500 turns

wound on a circular wooden frame of 15cm to 20 cm diameter, as shown in the figure. A

wooden plank about 100cm a long and 6cm to 8cm broad is fit horizontally inside the

wooden ring with equal lengths projecting to either side of the ring. A scale is fixes to plank

along its length and supported at its ends.

Connections are made as shown in the circuit diagram. Deflection magnetometer is

kept at the center of the coil. Electrical connections are turned off. The instrument as such is

rotated in such a way that the magnetic needle lies parallel to the plane of the coil. Then

rotate the deflection magneto meter until we get aluminum pointer in the ‘0’ – ‘0’ direction.

Keys are plugged in two diametrically opposite positions at the commutator and see that

deflection of the needle comes to be 60 degree. Then reverse the current direction plugging in

the keys in the other two slots of the commutator. If the deflection is 60 degree the set up is

correct. If the deflection is not equal on either side adjust the position of the instrument. This

set up of the instrument should not be disturbed until the end of the experiment.

Deflection in magnetometer is kept at the center of the coil and deflection of the coil

is noted down for both forward and reverse current. The magnetometer is moved towards.

East along the axis of the coil in steps of 2 cm and at time deflection for both forward and

reverse current is noted down until the deflection comes down to 20 degree. The same

process is repeated to west side also.

A graph is drawn between X along x-axis and the corresponding Tan θE and Tanθw

along y-axis. The Shape of the curve is as shown in the figure.

OBSERVATIONS:

Number of turns in the coil ‘n’___________ Be = 0.36 x 10 -4

tesla

Current through coil i=________________ Amp μ0 = 4π x 10 -7

henry / m

Radius of the coil a = ______________ cm 1 tesla = 1 weber/m2

Engin

eerin

g Ph

ysics Lab M

anu

al

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Malla Reddy Engineering College for Women Engineering Physics Lab

[22]

TABULAR COLOM

CALCULATIONS

RESULT

Magnetic induction at the center of the coil Experimental B =

Theoretical B =

PRECAUTIONS:

1. The line indicating magnetic meridian and its perpendicular line must clearly be

drawn on the table

S.No

Distance of

deflection

magneto-

meter from

the centre

of the coil

(x) meter

Deflection in the magnetometer towards

2

wE

Tanθ

Magnetic Induction

weber/m2

EAST side

WEST side

θ1

θ2

θ3

θ4

Mean θE

θ1

θ2

θ3

Θ4

Mean

θw

B=BHTan θ

23

22

2

0

2 ax

ainB

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[23]

2. The apparatus should not be distributed from its position after it has been arranged in

such a way that the coil in the magnetic meridian.

3. Ammeter and Rheostat should be kept away from the magnetometer so that their

fields should not influence deflection magnetometer.

4. Deflection in magnetometer should be moved on the groove of the apparatus in steps

of 2-3cm and while doing parallax error should be avoided.

5. Keep the key off while moving the magnetometer.

VIVA QUESTIONS:

1. What is the direction of the magnetic field at the center of the coil?

2. Where do we expect the field to be maximum in this experiment?

3. What is meant by magnetic meridian?

4. What is the use of Commutator?

5. What is the use of Rheostat?

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Malla Reddy Engineering College for Women Engineering Physics Lab

[24]

EXPERIMENT 6

EVALUATION OF NUMERICAL APERTURE OF A GIVEN

FIBER AIM:

To determine the numerical aperture (NA) of the given optical fiber

APPARATUS:

One or two meters of the step index fiber, Fiber optics kit

THEORY:

The numerical aperture of an optical fiber is the light gathering capacity, which is a

measure of the light collected by the optical fiber. It is defined as sine of the acceptance angle

(θ). Angle of acceptance is the maximum angle of incidence at the air – core interface so that

total internal reflection takes place at the core – cladding interface, and the light pass through

the fiber. Numerical aperture NA = sin θ

From the figure

1/2 1/2

2 2 22

2sin42

WBD W

AB L WL W

1/2

2 24

WNA

L W

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PROCEDURE:

Connect one end of the fiber to the LED light source and other end to the ZIG given in the

kit. Keep the light intensity knob at maximum for high intensity of light. Now keep the

screen in such a way that the light emerging from the fiber fall just inside the first circle.

Measure the distance between the fiber end and screen from the scale given in the zig. Note

down this value. Next make the light to fill the second circle exactly and measure the

corresponding distance between screen and fiber. Repeat the same for 3rd

, 4th

and 5th

circles.

These readings have to be tabulated against the diameter of the circles.

OBSERVATION TABLE:

S. No.

Distance

between fiber

end and the

screen

L (mm)

Radius of

the circle

W (mm)

NA

Acceptance

angle

)(sin 1 NA

(Degrees)

PRECAUTIONS:

1. Avoid bends in the cable.

2. Avoid cracks in the cable.

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RESULT:

The numerical aperture and acceptance angle of the given optical fiber is determined.

VIVA QUESTIONS:

1. What is the principle involved in optical fiber?

2. What is numerical aperture?

3. What is acceptance angle?

4. Is the refractive index of cladding is greater than core?

5. Mention different parts in OFC

6. What is critical angle?

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EXPERIMENT 7

OPTICAL FIBER - BENDING LOSSES

AIM:

To determine the loss caused in optical fibers in dB due to macro bending of the Fiber

APPARATUS:

Fiber Optic Kit, Optical cable of length 1m and 5m, mandrel

THEORY:

Attenuation due to macro bending in fibers

Attenuation is measured in decibels per kilometer (dB/Km), which is a logarithmic

unit. Loss of optical power = 10

log O

F

P

L P

dB/m

Where Po = Power launched in to the fiber, Pf = Power reached at the end of the fiber,

L = Length of the given optical fiber

PROCEDURE:

The transmission loss or attenuation of an optical fiber is perhaps the most important

characteristic of the fiber. Attenuation result from mainly scattering and absorption of light.

Attenuation also results from number of effects like, fiber bending, fiber joints, improper

cleaving and also splicing due to axial displacement and mismatch of core diameters of

fibers. Connect one end of the 1m optical fiber cable (OFC) to the LED light source and the

other end to the photo detector (PIN diode). Keep the light intensity knob at maximum. Insert

the leads of the dB meter at the output terminals of the optical power meter circuit. Turn on

the power switch and note down the light intensity in dB. This is the intensity of light without

down the light intensity with 3, 4 and 5 turns. Repeat the same with both one meter fiber and

five meter fibers.

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OBSERVATION TABLE:

Length of

fiber

S No No of turns Output

power

Loss =

Xi – X0

Loss/turn =

(Xi – X0)/i

1m X0

X1

X2

X3

X4

0

1

2

3

4

5m X0

X1

X2

X3

X4

0

1

2

3

4

RESULT:

The Bending Losses in 1m OFC = -------------------- dB

The Bending Losses in 5m OFC = -------------------- dB

VIVA QUESTIONS:

1. What are the various types of optical fibers?

2. What is meant by numerical aperture?

3. Define acceptance angle?

4. What makes an optical fiber free from EMI

5. Define total internal reflection?

6. What is the importance of cladding in an optical fiber?

7. What are the different types of losses in the optical fibers?

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EXPERIMENT 8

SINGLE SLIT DIFFRACTION USING LASER

AIM

To measure the width of the slit by using Single slit diffraction of laser

APPARATUS

Single slit, laser source, stand, meter scale and Traveling microscope

THEORY

The condition for diffraction maxima is a sin = n (A0)

Where is the angle subtended between the central bright maxima and the secondary

maxima, is wavelength of the laser source used, n is the order of the diffraction and ‘a’ is

the width of the slit. From the figure given below we get sin /y L . Using this value of

sinθ in the above equation we get .... .....y n L

a n or aL y

PROCEDURE

Place the single slit facing the laser source such that the rays incident on the slit.

Adjust the slit width approximately to 0.05mm such that we see clear diffraction pattern on

the screen or wall. Keep the distance of slit from wall to be 1M and let it be L. Distance

between the center and first intensity maxima is taken as y1 and the next y2 and so on.

Measure the distance from the center to the maxima on left and right side of the pattern up to

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5th

intensity maxima. Calculate the slit width by the above equation and compare it with slit

width (a) measured by travelling microscope.

Fig: 1 Optical bench setup of single slit laser

OBSERVATION TABLE

S. No

Distance

between

slit and

screen

L cm

Distance between central

maxima and first maxima

y cm

Slit width

Left Right Mean

Width of the slit (d):

Least Count of Traveling microscope = sleDivisionVernierScaofno

ivisionMainScaleDValueofOne

.

= cm

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Table:

Width of the slit, d = (Edge 1 ~ Edge 2) cm

PRECAUTIONS:

1. The room should be dark to observe the clear diffraction pattern.

2. The rope should be held straight enough while measuring (h) value.

RESULT:

WIDTH OF THE SLIT

Experimental =

Measured =

VIVA QUESTIONS:

1. Give the full form of LASER

2. What is meant by stimulated emission?

3. Explain spontaneous emission?

4. What is meant by diffraction?

5. What is meant by population inversion?

6. Give few applications of LASER.

S. No. MSR

a cm VCD

VCD X

LC

b cm

(a + b) cm

Edge 1

Edge 2

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EXPERIMENT 9A

LCR CIRCUIT - SERIES

AIM:

To study the frequency response of LCR series circuits and to determine the Resonant

Frequency of the circuit

APPARATUS:

LCR Trainer kit, Function generator, connecting wires

THEORY

Inductance (L), Resistance (R) and Capacitor (C) are connected in series with a source of AC

supply (signal generator). This circuit is called series resonance circuit. The resonant

frequency is given by the equation 1

2rf

LC

Quality factor of the circuit is given by 2 1

r rf fQ

f f f

Theoretically quality factor is given by 1 L

QR C

At resonance frequency, the resultant impedance of the combination is minimum and hence

the current is Maximum. So the frequency corresponds to maximum current is known as

resonant frequency.

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MODEL GRAPH

PROCEDURE:

Make the connections as shown in the circuit diagram. Turn on the signal generator. Set the

frequency selector switch at 20KHz and function selection switch at sine wave. Gradually

increase the frequency and see that the current is increasing and reaches to a maximum and

then decreases. If it does not happen something is wrong and has to be corrected. Now bring

the frequency down to 500Hz and note down the current. Increase the frequency in steps of

500Hz. Current will increase gradually with frequency and reaches to some maximum and

then starts decreasing. Reading has to be continued until the current reaches the minimum

value. A graph is plotted with current along the y axis and frequency along the x axis. From

the graph frequency corresponds to maximum current is obtained

OBSERVATION TABLE:

S No Frequency Current

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CALCULATION:

Theoretical Value:

Resonant frequency of the series circuit is given by Hz

Quality Factor:1 L

QR C

Practical value:

Resonance frequency of the series circuit is fo = ------------------- Hz.

Quality Factor:

Q = fo / Δf , Δf = f2 – f1 , Δf = Band Width

RESULT:

Verified the Resonance frequency of LCR series circuit

Resonant frequency

Theoretical value =

Experimental value =

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EXPERIMENT NO 9B

LCR : PARALLEL RESONANCE

AIM:

To study the frequency response of LCR parallel circuits and to determine the

Resonant Frequency of the circuit

APPARATUS:

LCR Trainer kit, Function generator, connecting wires

THEORY

Resonant frequency of the parallel LCR circuit is given by the equation 2

2

1 1

2

Rf

LC L

When R is very small resonant frequency 1

2f

LC

Quality factor 1 L

QR C

CIRCUIT DIAGRAM:

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Model graph

PROCEDURE:

Make the connections as shown in the circuit diagram using the prescribed values of L, C

and R. keep the frequency at 500Hz and gradually increase. If the current decreases and

reaches to a minimum and then increases the circuit is correct. Note down the value of

current for frequency from 500Hz to the next frequency at which current again becomes

maximum. Plot a curve of frequency versus current. The minimum of current gives the

resonant frequency.

OBSERVATION TABLE:

S. No Frequency (KHz) Current (µA)

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CALCULATION:

Theoretical Value:

Resonant frequency of the parallel circuit is given by

1

2f

LC

Quality Factor:

1 LQ

R C

Practical value:

Resonance frequency of the parallel circuit is fo = ------------------- Hz.

RESULT:

Verified, the Resonance frequency of LCR parallel circuit

Resonant frequency

Theoretical value =

Experimental value =

VIVA QUESTIONS:

1. What is tuning?

2. What is resonance?

3. What is a rejecter circuit?

4. What is an acceptor circuit?

5. What are half – power frequencies?

6. What is meant by Bandwidth?

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EXPERIMENT 10

CR CIRCUIT

AIM:

To determine the time constant of the given RC circuit

APPARATUS:

RC circuit kit, connecting probes and stop watch

FORMULAE:

(i) Charging:

The voltage across the capacitor, during the charging phase, Vc = V0

RC

t

e1

At time t = RC, Vc = Vo

e

11 = 0.63 Vo

(ii) Discharging:

The voltage across the capacitor, during the discharging phase, Vc = Vo {exp [ - t / (RC)] }

Vc = V0

RC

t

e

At time t = RC, Vc = Vo

e

1 = 0.37 Vo

The time constant T = RC

Where ‘R’ resistance and ‘C’ capacitance

PROCEDURE:

Make the connections as shown in the figure with prescribed values of C and R. Keep the

switch in the charging position and simultaneously starts the stop watch. Starting from zero

second note down the voltmeter reading at intervals of five second till the voltmeter reading

becomes maximum constant value. Then keep the switch at discharging position and

K R

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simultaneously start the stop

watch. Note down the

voltmeter reading at intervals

of five second till it reaches

very near to zero. Plot graphs

taking voltage along the Y

axis and time along X axis.

From the charging graph find

out the time corresponds to

0.63V0. this the time constant for the circuit. From the discharging graph find out the time

corresponds to 0.37V0. This will give the time constant.

MODEL GRAPH

OBSERVATION S

(i) CHARGING:

R = Ω

C = µF

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S. No.

Time required

t sec

Voltage across the

Capacitor,

Vc Volts

Result: The time constant of the given RC circuit = RC =

(ii) DISCHARGING

R = Ω

C = µF

S. No.

Time required

t sec

Voltage across the

Capacitor,

Vc Volts

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RESULT:

The exponential decay of current in a circuit containing resistance and capacitance is

studied and the RC time constant =

VIVA QUESTIONS:

1. What is meant by reactance of an inductor?

2. Give a brief description about impedance of a circuit ?

3. What is meant by RC time constant?

4. Define resonance?

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EXPERIMENT 11

NEWTON’S RINGS

AIM:

To measure the wavelength of sodium light using Newton's rings method

APPARATUS:

Traveling microscope, plane glass plate and Plano convex lens attached in a frame,

sodium vapor lamp, Magnifying lens, and spherometer.

FORMULA:

Wave length of sodium light is given by

)(4

22

nmR

DD nm

A

0

Where Dm, Dn are diameters of mth

, nth

rings respectively R is the radius of curvature of the

Plano convex lens

Where 2

6 2

l hR

h

(h is the thickness or height of the curved surface and ‘l’ is the

length between the legs of the spherometer) λ is the wave length of the sodium vapor light

PROCEDURE

In this experiment the condition for interference maxima used to determine the wavelength of

a light source. If a clean convex lens is placed on a clean glass plate (optically flat) and

viewed in monochromatic light, a series of rings may be seen around the point of contact

between the lens and the plate. These rings are known as Newton's rings and they arise from

the interference of light reflected from the glass plate and from the lower curved surface of

the lens. The experimental set-up is shown in figure.

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Fig: 2

Newton’s

Rings

Turn on the sodium vapor lamp. Place the Plano convex lens on the plane glass plate with

curved surface in contact with the glass plate and place this system under another plane glass

plate fixed with 450 inclination so that light coming from the sodium vapor lamp will be

reflected towards the lens plate assembly. Bring the travelling microscope just above the

inclined glass plate and focus at the center of contact between the lens and glass plate. Now

dark and bright concentric circular rings will be seen. Bring the cross wire of the microscope

exactly at the center of the first ring. While looking through the microscope move the

microscope cross wire to one side and coincide with 20th

ring by rotating the fine adjustment

screw. Note down the vernier readings for

20th

, then 18th

, 16th

and so on to 20th

ring

on other side.

Measure the radius of curvature of the lens

using spherometer. Plot a graph taking D2 on

Y-axis and No of rings on X-axis. From

graph calculate the values of Dm2 , Dn

2 and

find the wavelength of the given sodium

light from the given formula

OBSERVATIONS

Least count of the microscope =

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TABLE: 1

To find diameter of the Rings:

S. No No

of

rings

Travelling Microscope reading Diameter

D =

(L ~ R) D2

Left (L) Right (R)

M.S.R

a

V.C (V.C x

L .C)

b

Total

(a+b)

M.S.R

a

V.C (V.C x

L.C)

b

Total

(a+b)

1

2

3

4

5

6

7

8

9

10

20

18

16

14

12

10

8

6

4

2

TABLE: 2

To find the radius of curvature of Plano convex lens (using spherometer)

Least count of the spherometer =

S. No P.S.R

(a)

Head scale

coincidence (n)

n x L.C

(b)

Total (h)

(a+b)

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Thickness of the bulging partition of the plano of convex lens =

The radius of curvature of Plano convex lens R = ------------------ cm

RESULT:

The wave length of the given sodium light is = --------------------- nm

PRECAUTIONS:

1. There should not be any back lash error while taking readings of microscope.

2. The zero error should be minimized in the spherometer.

3. Should not tight the screws of frame of glass plate and Plano convex lens.

4. Should not touch the rack and pinion screw of microscope after the initial

adjustments.

VIVA QUESTIONS:

1. How do we get interference pattern and why there is a dark spot at the center?

2. What is the least count of the spherometer?

3. What is the least count of the traveling microscope?

4. Explain thin film interference?

5. Define least count?

6. Define wavelength?

7. Classify the types of waves?

8. Give the value of refractive index of air?

9. Explain normal incidence?

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EXPERIMENT 12

ENERGY GAP OF A MATERIAL OF PN-JUNCTION DIODE

AIM:

To determine the energy band gap of a material of a semiconductor p-n junction diode

APPARATUS:

Semiconductor diode, power supply, Thermometer, Micro ammeter, Voltmeter,

Connecting wires

THEORY:

A p-n junction is created when a p-type semiconductor and n- type semiconductor are

brought into contact. When a voltage is applied to the p-n junction, current will flow through

the junction. The current I flowing through a p-n junction diode is given by

I = Io [exp (eV/KBT) – 1]

Energy band gap is given in electron volt by the equation 19

2.303 2 ( )

1.6 10

BG

k dy dxE eV

Where KB is the Boltzmann constant and (dy/dx) is the slope of the Log I0 and 1/T graph.

I0 - reverse saturation current and T- absolute

temperature

PROCEDURE

Connections are made as shown in the

figure. A small reverse bias voltage (less than

2V) is applied to the diode by adjusting the

voltage knob. Thermometer is fixed at its

position. Heater is turned on. As the

temperature rises for every five degree rise

current has to be recorded from 40 degree to a

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maximum of 70 degree. At 70 degree of temperature turn of the heater and allow the

instrument to cool. During cooling note down the current value in every five degree decrease

of temperature staring from 70 degree until the temperature falls to 40 degree. Plot a graph

by taking the log of current value along the y axis and 1/T along the x axis either for heating

or for cooling whichever is seems to be more reliable. Slope of the graph has to be used for

calculation.

OBSERVATION TABLE:

S No Temperature

in degree

Celsius

Temperature

Kelvin (T)

(Io) Reverse

saturation

current(µA)

Log(Io) 1/T

RESULT:

Energy gap of Si, Eg = ---------------------- eV

VIVA QUESTIONS:

1. What is Forbidden energy gap?

2. What are intrinsic and extrinsic semiconductors?

3. Why do we prefer semiconductors to conductors when conductors have got better

conductivity?

4. What is positive temperature coefficient and negative temperature coefficient