BE - 201 - Engineering Physics Practical Experiments

EXPERIMENT NO. 1

1. Aim :

To determine the frequency of A.C. mains by using an electric vibrator. 2. Apparatus :

Electric vibrator

Table lamp

Pulley

Weight box

Fishing cord

A.C. source

3. Theory :

When a cord of mass per unit length m is connected to the vibrating rod of the vibrator and stretched with a tension T, the cord vibrators in segments. If the length of the cord is then adjusted until the nodes are clearly marked, the frequency of the stretched string is the same as of the vibrating rod which is vibrating with the frequency of A.C. Mains. Its frequency of vibrating is given by :

η = 12l � Tm

- and this is also frequency of A.C. mains

EXPERIMENT NO. 1

4. Procedure :

1. Switch on current and see that the rod of the electric vibrator begins to vibrate. 2. Adjust the length of the rod till its free ends attain the vibrations of maximum

amplitude. After length of the vibrating cord by shifting the vibrator till the nodes are clearly defined.

3. Mark the position of extreme node leaving out the first and last loop. Measure the

length of the vibrating cord and divide it by the no. of loops to get ‘l’ for some tension. 4. Take more sets by altering the length of the cord. Calculate the mean total tension

applied to the cord. 5. Repeat the experiment with different tensions.

5. Observation :

Mass per unit length = gms / cm Mass of the pan = gms

No. Of loops

Length of cord

Length of one loop

Mass of pan

Mass on pan

Total mass

Tension T=Mg

(N) (L cm) (L/N cm) (gms) (gms) (M gms) (gmcm/sec2)

1.

2.

3.

4.

5.

EXPERIMENT NO. 1

6. Calculation :

Calculate six η1, η2, η3, η4, η5, η6, by using below formula by changing the value of T & l according to table :

η = 12l � Tm

mean η = η1 + η2 + η3 + η4 + η5 + η66

% error = Standard value − Experimental valueStandard value ∗ 100 %

7. Result :

The frequency of A.C. mains = cycle / sec or Hz

8. Precautions :

1. The length of the steel rod must be initially adjusted so that it vibrates in resonance with A.C. frequency. This is obtained when the free end of the rod vibrates with maximum amplitude.

2. There should be no friction in the pulley. 3. The cord should posses’ fairy constant mass per unit length. 4. The nodes and antinodes on the cord should be sharply defined.

EXPERIMENT NO. 2

1. Aim :

To plot the characteristic curve of semiconductor diode. 2. Apparatus :

Semiconductor diode

Voltmeter

Ammeter

A regulated power supply

3. Theory :

1. Semi-conductor diode :

A diode is a two terminal device. One terminal being known as anode and other known as cathode. A diode should work like a switch. When its anode made positive with respect to its cathode, the diode should act like a closed switch and when its anode made negative with respect to its cathode, acts like an open switch. When a D.C. voltage is applied to a device, the device is said to be biased. A p-n junction can be biased in two ways :

1. If the positive terminal of the D.C. supply is connected to p-region and negative terminal is connected to n-region (cathode), the diode is said to be forward biased.

2. If the positive terminal of the D.C. supply is connected to n-region and negative

terminal is connected to p-region (cathode), the diode is said to be reverse biased.

2. Forward bias characteristics :

In forward bias the diode current increases rapidly as the potential across the diode is increased. The diode starts conducting only after a certain voltage known as threshold voltage. In the forward biased condition, majority charge carriers are responsible for conduction. The number of these charge carriers injected at the junction increases with the voltage and thus the current increases with voltage.

EXPERIMENT NO. 2

3. Reverse bias characteristics :

Under reverse bias condition minority charge carriers take part in the process of conduction. Here the leakage current flows in the circuit. This current is known as reverse saturation current. It increases rapidly in the initial stage due to an exponential decrease of diffusion current with increasing reverse voltage.

4. Procedure :

1. Forward bias :

1. Make the connection as shown in the circuit. 2. Vary the inbuilt D.C. supply voltage in steps of 0.1V and note down corresponding

voltmeter and ammeter readings. 3. Plot the graph of voltage (on x-axis) Vs current I (on y-axis).

2. Reverse bias :

1. Make the connection as shown in the circuit. 2. Put the voltmeter range switch to 50V and ammeter range switch to 200 µA. 3. Vary the supply voltage in steps of 1V and note down corresponding voltmeter

and ammeter readings. 4. Plot the graph of voltage (on x-axis) Vs current I (on y-axis).

A

V

A

V

EXPERIMENT NO. 2

5. Observation :

1. Forward bias :

Voltage (V) Current (mA)

Division Least count Total Division Least count Total

1.

2.

3.

4.

5.

2. Reverse bias :

Voltage (V) Current (mA)

Division Least count Total Division Least count Total

1.

2.

3.

4.

5.

6. Result :

Forward and reverse bias characteristics of semiconductor diode is plotted on the graph.

EXPERIMENT NO. 2

7. Precautions :

1. In the forward bias the p terminal of diode should be at positive potential an N terminal at negative potential. While in reverse bias, the P terminal of diode should be at negative potential and N terminal at the positive potential.

2. The positive marked terminal of voltmeter and ammeter should always be connected to

the positive terminal of the battery. 3. Current should not be passed for a long duration through the diode otherwise it will get

heated. 4. Increase the voltage gradually.

EXPERIMENT NO. 3

1. Aim :

To plot the characteristic curve of Zener diode. 2. Apparatus :

Zener diode

Voltmeter

Ammeter

A regulated power supply

3. Theory :

1. Semi-conductor diode :

A diode is a two terminal device. One terminal being known as anode and other known as cathode. A diode should work like a switch. When its anode made positive with respect to its cathode, the diode should act like a closed switch and when its anode made negative with respect to its cathode, acts like an open switch. When a D.C. voltage is applied to a device, the device is said to be biased. A p-n junction can be biased in two ways :

1. If the positive terminal of the D.C. supply is connected to p-region and negative terminal is connected to n-region (cathode), the diode is said to be forward biased.

2. If the positive terminal of the D.C. supply is connected to n-region and negative

terminal is connected to p-region (cathode), the diode is said to be reverse biased.

2. Forward bias characteristics :

In forward bias the diode current increases rapidly as the potential across the diode is increased. The diode starts conducting only after a certain voltage known as threshold voltage. In the forward biased condition, majority charge carriers are responsible for conduction. The number of these charge carriers injected at the junction increases with the voltage and thus the current increases with voltage.

EXPERIMENT NO. 3

3. Reverse bias characteristics :

Under reverse bias condition minority charge carriers take part in the process of conduction. Here the leakage current flows in the circuit. This current is known as reverse saturation current. It increases rapidly in the initial stage due to an exponential decrease of diffusion current with increasing reverse voltage.

4. Zener diode :

It is a p-n junction diode in which the quantity of impurity doped is more than that of an ordinary diode. If a battery connected at the terminal of zener diode such that the positive terminal of the battery is connected to p and negative to N, it is said to be in forward bias. The holes of p- region are repelled by the positive electrode and more towards the junction and electrons of N- region are repelled by the negative electrode and move towards the junction. Thus, electric conduction takes place at junction. A potential difference across the diode increases, the current in the circuit also increases. When the positive terminal of the battery is connected to N and negative connected to p, it is said to be in reverse bias. The holes of P region move away from the junction and similarly the electron of N region move away from the junction. Thus no current flows in the reverse bias due to majority charge carriers. But the minority charge carriers of p region and holes of N region move towards the junction due to which a very feeble current flows. On increasing the reverse voltage, a stage is reached when the current suddenly increases. This potential is called breakdown voltage. The reason is that when the reverse electric field at the junction increases, the covalent bond break and a large number of charge carriers are produced. This is called zener breakdown.

CIRCUIT DIAGRAM- _

A A

V V

EXPERIMENT NO. 3

4. Procedure :

1. Forward bias characteristics :

1. Make the connection as shown in the circuit. 2. Vary the forward voltage V in steps and note down the corresponding value of

current. 3. Plot the graph of voltage (on x-axis) Vs current I (on y-axis).

2. Reverse vias characteristics :

1. Connect the zener in reverse polarity of the supply in the given terminal. 2. Increase the supply voltage in steps and note the corresponding readings of the

ammeter. 3. At a particular voltage Vz the current is maximum. Plot the graph between current

and voltage.

5. Observation :

1. Forward bias characteristics :

Voltage (V) Current (mA)

Division Least count Total Division Least count Total

1.

2.

3.

4.

5.

EXPERIMENT NO. 3

2. Reverse vias characteristics :

Voltage (V) Current (µA)

Division Least count Total Division Least count Total

1.

2.

3.

4.

5.

6. Result :

Forward and reverse bias characteristics of zener diode is plotted on the graph. 7. Precautions :

1. In the forward bias the p terminal of diode should be at positive potential an N terminal at negative potential. While in reverse bias, the P terminal of diode should be at negative potential and N terminal at the positive potential.

2. The positive marked terminal of voltmeter and ammeter should always be connected to

the positive terminal of the battery. 3. Current should not be passed for a long duration through the diode otherwise it will get

heated. 4. Increase the voltage gradually.

EXPERIMENT NO. 4

1. Aim :

To determine the wavelength of violet and green light by using a diffraction grating. 2. Apparatus :

Plane transmission grating

mercury lamp

reading lamp

reading lens

3. Theory :

When a parallel beam of monochromatic light of wavelength λ (from the collimator) is incident normally on a grating. By Huygens’s principle each point of slit emits out secondary wavelets in all directions which interfere and get focused in the focal plane of a convex lens. The path difference between the diffracted waves at an angle θ from the corresponding points of two consecutive slits is (e+d) sinθ . When this path difference is equal to integer multiple of wavelength λ, principal maxima are obtained.

(e+d).sin θ = nλ where n= 0, 1, 2………………..n is called order of spectra For n = 0, we get zero order (or central) maxima

For n = ±1, ±2……….we get first order, second order maxima respectively on either side of zero order maxima

Thus knowing the grating element (e + d) and the angle of diffraction θ in a particular order n, the wavelength λ of light can be calculated. Now if white light is made incidence on a grating, in each order the value of θ will be different, corresponding to different wavelengths present in the incident white light. Thus we get spectrum in each order. The first order (n = 1) principal maxima of wavelengths in the incident light form the first order spectrum. Similarly the second order (n = 2) principal maxima of wavelengths in the incident light form the second order spectrum. Since angle of diffraction θ=0 for the principal maxima of all wavelengths corresponding to n=0, therefore the zero order maxima is white in the direction of incident light (on either side of which there are first order and second order spectrum).

Formula used :

wavelength λ of a spectral line : (e+d).sin θ = nλ e+d = 2.54 / N

λ = [(2.54 / N).sin θ] / n

EXPERIMENT NO. 4

e = grating element

θ = angle of diffraction

n = order of spectrum

N = number of lines ruled per inch on grating

G1 = first order green

V1 = first order violet

G2 = second order green

V2 = second order violet

4. Procedure :

1. The telescope is brought in the lines of collimator and the image of slit is focused at the point of intersection of cross wire. This position of telescope on the circular scale is noted.

2. Then the telescope is turned exactly by 90° from the position and is clamped, so that

axis of telescope becomes exactly normal to the axis of collimator. 3. Now the grating is mounted on the table. Table is then gradually rotated till the image

of slit formed by light reflected from the grating surface is focused at the point if intersection of cross wire in the telescope. In this condition the plane of grating makes an angle 45° with the incident light.

G2

@1

V2

Second order

First order

Zero order

G1

V1

Second order

First order

V1

G1

G2

V2

G

EXPERIMENT NO. 4

4. Now the grating is turned 45° or 135° such that the ruled surface of grating comes towards the telescope. The light incident from the collimator is normal on the grating. The rulings on the grating are adjusted parallel to the slit.

5. The telescope from the position of direct image of the slit is rotated towards left till the

first order spectrum is seen. The telescope is then gradually rotated to coincide the violet and green spectral lines and the readings of both veniers V1 and V2 are noted.

6. Then the telescope is further moved in the same direction to bring the second order

spectrum in the field of view and again the readings of both verniers V1 and V2 are noted by coinciding the vertical cross wire on the spectral lines of same colors successfully.

7. Now the telescope is turned on the right side of the direct image of slit and again the

readings of both the verniers V1 and V2 are noted for same spectral lines in the first and second order spectrum.

8. Then for the spectral line of each color, find the difference of readings of either side of

slit for the same vernier V1 (or V2). Take the mean and find the half of it which will give the angle of direction θ for the spectral line of that colour.

9. Note the number of lines ruled per inch on the grating.

5. Observation :

Least count of main scale = 0.5°

Total number of vernier division = 30°

Least count of vernier scale = 0.5°/30’ = 30’/30’ = 1’

EXPERIMENT NO. 4

Order of spectrum

Colour of spectral line

Vernier scale reading

Position of telescope (R)

Position of telescope (L)

2θ = θ2 - θ1

Angle of diffraction θ

MSR VSR TR MSR VSR TR

First order

Violet V1

V2

Green V1

V2

Second order

Violet V1

V2

Green V1

V2

6. Calculation :

(e+d).sin θ = nλ

λ = !e + d" sin θn (for first order n = 1 and for second n = 2)

The no. of lines ruled per inch grating N = 15000 Grating element (e+d) = 2.54/15000 cm 7. Result :

The wavelength of violet and green colour for the given source of light :

Colour of spectral line Observed wavelength (in Å)

Standard wavelength (in Å)

Percentage error

Green

Violet

EXPERIMENT NO. 4

8. Precautions :

1. The mechanical adjustment of the telescope should be correct. 2. The optical adjustment of the spectrometer must be made correctly. 3. The slit used should be as narrow as permissible. 4. In handling the grating do not touch the faces of glass. 5. The light incident from the collimator should fall normal on the grating.

EXPERIMENT NO. 5

1. Aim :

To study the properties of LASER. 2. Apparatus :

He-Ne LASER

Optics lab

Screen

Duster

3. Theory :

1. LASER :

LASER is the acronym for light Amplification by Stimulated Emission of radiation. The characteristic of a LASER light are monochromaticity ,coherence in time and space, narrow divergence of the beam and high intensity. LASER light like any other light is invisible to our eyes unless it is traveling in a direction which will permit it to enter the eye and fall on the retina .When small particles. This scattered light enables us to see the LASER beam. It will be observed that whenever scattered occurs there will also be some absorption of the LASER beam, and it will weaken in intensity as a result.

2. He-Ne LASER :

The He-Ne LASER was developed in 1961 by Ali Javan. The lasing medium in the He-Ne LASER is a mixture of about 85% helium and 15% neon, with neon providing the lasing action. It employs a four level pumping scheme. Transitions from level E3 to E4 and E4 toE1 are accomplished through a four photon transitions in which energy is transferred mainly through heat .Pumping of neon to an excited state is not done directly by the energy source .Rather, indirect pumping is exciting atoms of helium, which then transfer energy to the new atom by way of electron collision.

EXPERIMENT NO. 5

4. Procedure :

1. Shake chalk dust by blackboard eraser in front the LASER and record of the scattering effects that are observed.

2. Allow LASER light to pass through a prism.

3. Observer the spectrum of colours that appears.

4. Allow beam to pass through optical fibre.

5. Allow beam to pass through polarizer and observer effect.

6. Allow beam to pass through divergence lens and observe the effect.

7. Allow beam to pass through different colours filter and observe the effect.

8. Allow beam to pass through diffraction grating of different grating elements.

9. Change the distance between source and the screen and note the effect on LASER

spot intensity.

10. Focus the beam on the letter .Note the focus effect.

5. Observation :

1. When LASER beam is passes through the prism it does not disperse.

2. When LASER beam is pass through the optical fibre it under goes total internal reflection.

3. When dust particle is spread up in the path of LASER beam .It path is visualized due to

scattering.

4. When it is passé through the diverging lens it get diverge but less diverge.

5. When the distance between the LASER source and screen is changed its intensity does not vary.

6. When LASER passé through polarizer it intensity is change for max to min.

7. It is focused on the single point.

EXPERIMENT NO. 5

8. Diffraction pattern is found when LASER passed through the diffraction grating and there pattern are change for different grating elements grating.

9. When it is passed through the red and yellow filter is intensity does not change and for

blue colour filter it become minimum but for green colour filter it intensity become zero.

6. Result :

1. It is a monochromatic light beam.

2. It is a highly intense light beam.

3. He-Ne is less diverse light beam.

4. He-Ne is highly focused beam.

5. He-Ne LASER beam follows all properties of the light such as : I Scattering

II Diffraction

III Polarisation

IV Total internal reflection

6. Green colour is the best absorbent of He-Ne LASER.

7. Precautions :

1. Do not look into LASER or stare at bright mirror like reflections of the beam.

2. If the beam travels a long distance keep it close to the ground or overhead so that it does not cross walkways at eye level.

3. Never point a LASER on anyone.

4. Make sure the LASER is always secured on a solid foundation.

5. LASER employs high voltages so never open the housing.

EXPERIMENT NO. 6

1. Aim :

To determine the Hall coefficient of given semiconductor. 2. Apparatus :

Electromagnets

Power supply of electromagnet

Gauss meter for measuring magnetic flux

Germanium crystal

Stand

Constant power supply

3. Theory :

When a current carry conductor is placed in the cross magnetic and electric field a electric field is induced in the conductor which is perpendicular to the applied electric and magnetic field. This effect is known as Hall Effect and induced potential difference is known as Hall voltage.

4. Procedure :

1. Connect the power supply to the electromagnets .Switch on power supply adjust the current (say 1 amp).

2. With the help of Gauss meter measure the magnetic field if it is 1000 gauss then carry

the next step otherwise by adjusting the electromagnets coil adjust magnetic field at 1000 gauss.

3. Connect the Hall crystal to constant current power supply in their respective sockets. 4. Switch on the power supply and adjust the current (Ix). 5. There may be some voltage in the (mv) meter even outside the magnetic field this is

due to imperfect alignment for four contacts of Ge,Hall voltage should alignment for four contacts of Ge crystal and is generally known as zero field potential in case it’s value is compare to Hall voltage it should be adjusted to a minimum possible .In all case this error should be subtracted from the Hall voltage reading.

EXPERIMENT NO. 6

6. Now place the probe in the magnetic field as shown in figure and switch on the electromagnetic power supply and adjust the current to any desired value .Rotate the Ge crystal probe till it become perpendicular to magnetic field. Hall voltage (VH) becomes maximum in this adjustment.

7. Change the value of (Ix) insteps and note corresponding value of (Ix) and (VH). Take

many reading then plot a graph in VH and Ix values. It will be straight line .whose slope will be given by VH / Ix.

5. Observation :

Thickness of crystal = 0.55 cm Magnetic field = 1000 gauss

Hall Current (Ix) Hall Voltage (VH)

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

EXPERIMENT NO. 6

6. Calculation :

slope = y1 − y2x2 − x1

Hall coefficient = V+tBIx

7. Result :

The Hall coefficient of given semiconductor = volt cm / gauss amp

8. Precautions :

1. Handle the Ge crystal with care, it can break. 2. Handle the probe of gauss-meter with care it may damage in mishandling. 3. Does not use electromagnetic continuous at full current .It may be start heat. 4. Gap between poles of electromagnet must be remaining fix during one reading.

EXPERIMENT NO. 7

1. Aim :

To study the characteristic of the Geiger Muller counter. 2. Apparatus :

Triode geiger counting System (GCS)

GM tube and a radioactive source

3. Principle :

When a gamma ray (or a charge particle) enters the gas filled GM tube, it ionizes the gas inside it and the electric field applied between the electrodes drift, the electrons towards the anode. The elections thus collected at the anode are counted various applied voltage using Geiger Counting System. A graph is plotted for applied voltage vs. corrected counts (NB - N) and hence the operating voltage is determined from the graph.

4. Procedure :

1. The Geiger counter system GCS is connected to the GM tube, which is mounted on a stand (vertical mount).

2. The radioactive source is placed in the source holder at a distance of about 5cm from

the tube. 3. The GCS is switched on and the counter is reset to zero. 4. The high voltage is increased slowly from minimum until the counting just starts. This

threshold voltage is noted. 5. The present time is set to be 20 seconds and the number of counts for this voltage is

recorded. 6. Now the voltage (V) is increased in steps (say50V) and the number of counts (N) is

recorded every time. 7. Increasing the voltage is stopped when the count rate suddenly increases. Any further

increase in voltage may damage the GM tube .The number of count starts decreasing at this point. In this particular case the voltage should not be increased more than 950V.

EXPERIMENT NO. 7

8. The voltage is checked on digital multimeter at range 1000V DC after every setting before taking readings the meter lead is disconnected so as to avoid unnecessary load across the G.M. tube.

9. By removing the radioactive source the background count (NB) is recorded for 20

seconds.

10. A graph is plotted for applied voltage (V) vs. corrected count rate (NB-N) .the threshold voltage and the limits of the Geiger plateau are marked .The midpoint of the plateau region gives the operating voltage of the tube. The tube must always be operated with this voltage when it is used.

Tungsten wire Cu tube Argon (90%) +C2H5OH (10%) Counting system High tension battery

G.M. Counter

EXPERIMENT NO. 7

5. Observation :

S.No. Applied voltage (V) volts

No of count without source N/20sec

No. of count with source NB/20sec

Corrected counts (N - NB)20sec

1 450

2 500

3 550

4 600

5 650

6 700

7 750

8 800

9 850

10 900

11 950

Plot graph between applied voltage (V) and corrected counts (N-NB).

Corrected Count (N-NB)/20sec

Applied voltage (V) volts

EXPERIMENT NO. 7

6. Result :

Threshold voltage = volts Operating voltage = volts

7. Precautions :

1. Reset counter after every set of reading by pressing reset switch. 2. Take out Beta source after every reading with the help of fork. 3. Do not hold beta source with fingers directly or put it vicinity to human body.

EXPERIMENT NO. 8

1. Aim :

To determine the refractive indices of the given calcite prism material corresponding to ordinary and extra-ordinary rays by using sodium light.

2. Apparatus :

Calcite prism

A spectrometer

A sodium vapour lamp

3. Theory :

Light passing through a calcite crystal is split into two rays. This process, first reported by Erasmus Bartholinus in 1669, is called double refraction. The two rays of light are each plane polarized by the calcite such that the planes of polarization are mutually perpendicular. For normal incidence (a Snell’s law angle of 0 ), the two planes of polarization are also perpendicular to the plane of incidence. For normal incidence (a 0angle of incidence), Snell’s law predicts that the angle of refraction will be 0 . In the case of double refraction of a normally incident ray of light, at least one of the two rays must violate Snell’s Law. For calcite, one of the two rays does indeed obey Snell’s Law; this ray is called the ordinary ray (or O-ray). The other ray (and any ray that does not obey Snell’s Law) is an extraordinary ray (or E-ray). For ordinary rays the vibration direction, indicated by the electric vectors in our illustrations, is perpendicular to the ray path. For extraordinary rays, the vibration direction is not perpendicular to the ray path. The direction perpendicular to the vibration direction is called the wave normal. Although Snell’s Law is not satisfied by the ray path for extraordinary rays, it is satisfied by the wave normal of extraordinary rays. In other words, the wave normal direction for the refracted ray is related to the wave normal direction for the incident ray by Snell’s Law.

EXPERIMENT NO. 8

4. Procedure :

1. Setting up of the spectrometer :

1. The spectrometer base is levelled using a spirit level. 2. The prism table is levelled first with the spirit level. 3. The spectrometer is set with the collimator towards the light source. The slit is

adjusted to be as narrow as possible. The image of the slit is adjusted to be at the center of the field of view.

4. The eyepiece of the telescope is adjusted such that the crosswire are seen

distinctly. 5. The telescope and the collimator are adjusted for parallel rays using Schuster's

method. 6. The prism table is levelled optically with the help of prism. 7. The least count of the spectrometer is determined.

2. Measurement of refracting angle ‘A’ of the prism :

1. The quartz (or calcite) prism is kept on the prism table with its refracting edge at the center and pointing towards the collimator. The light from the collimator is incident upon both the refracting surfaces simultaneously and they give rise to reflected images.

2. The telescope is turned first to one side to receive the reflected image. When the

image is in the field of view, the telescope is clamped. With the help of the tangential screw, the vertical cross wire of the telescope is slowly moved and it is coincided with the image of the slit. In this position, the reading of the main scale and vernier scale of both windows are read and recorded in Observation Table 1.

3. The telescope is unclamped and rotated to the other side till the reflected image

from the second refracting surface of the prism comes into the field of view. When the image of the slit is sighted, the telescope is clamped and with the help of tangential screw, the vertical crosswire is made to coincide with image of the slit. Again the readings of scales from both the windows are recorded in Observation Table 1.

EXPERIMENT NO. 8

4. The Procedure is repeated thrice. From readings, the angle of the prism is determined. The angle of the prism is equal to half of the difference between the readings in the two positions of the telescope.

3. Measurement of the angle of deviation :

1. The prism table is rotated slowly till the prism base becomes nearly parallel to the collimator beam. The telescope is turned to get the refracted image on the vertical cross wire. Two yellow images of the slit are observed. One yellow image of the slit is coincided with vertical cross wire.

2. Now the prism table is rotated so that the image moves to one side. The

telescope is moved with the help of the tangential screw so that it follows the image. Finally a position is reached when the image becomes nearly stationary. A further rotation of the prism table in the same direction makes the spectral line recede. By moving the prism table slowly twice or thrice, the stationary position of the yellow line is ascertained. The cross wire of the telescope are made to coincide with the yellow line. This is the position of minimum deviation. The position of the telescope is read on both windows. The readings are recorded in Observation Table 2.

3. Now the second yellow image of the slit is coincided with the vertical cross wire.

The procedure in step 6 above is repeated to determine the minimum deviation position corresponding to the second image.

4. The prism is removed from the prism table and the telescope is brought to view

the image of the slit directly and its position is read and recorded in Observation Table 2. This position corresponds to that of the undeviated image.

5. The angle through which the telescope has been rotated from undeviated

position to deviated position gives the angle of minimum deviation.

5. Observation :

Sr. No

Venire

Reflection from first face

Reflection from second face

Difference a - b = θ (Deg.)

Mean theta (Deg.)

A = theta /2 (Deg)

MSR (Deg.)

VSR T.R. (Deg.) (a)

MSR (Deg.)

VSR T.R. (Deg.) (b)

V1

V2

EXPERIMENT NO. 8

Venire

Reflection Image reading

Direct Image reading Difference B

= a - b (Deg.)

Mean of Deviation angle Dm=B/2

MSR (Deg.)

VSR T.R. (Deg.) (a)

MSR (Deg.)

VSR T.R. (Deg.) (b)

O-Ray

V1

V2

E-ray

V1

V2

6. Calculation :

no = refractive index for the ordinary ray

ne = refractive index for the extra-ordinary ray

A = angle of prism

(Dm)e = angle of minimum deviation for e-ray

(Dm)o = angle of minimum deviation for o-ray

EXPERIMENT NO. 8

% error = Standard value − Experimental valueStandard value ∗ 100%

7. Result :

The refractive index for ordinary ray (n0) = with % error The refractive index for extra-ordinary ray (ne) = with % error

8. Precautions :

1. The telescope and collimator should be individually set for parallel rays by Schuster's method.

2. Slit should be made as narrow as possible. 3. Both windows should be read. 4. Prism should be properly placed on the prism table for measurement of angle of the

prism as well as for the angle of minimum deviation.

EXPERIMENT NO. 9

1. Aim :

To determine the energy band gap of a semiconductor using a junction diode. 2. Apparatus :

Thermometer

Oven

P-N junction diode

D.C. Power supply

3. Theory :

A semiconductor doped or undoped always posses an energy gap between in conduction and valence band for the conduction of electricity so that it goes from valence band to the conduction band. When PN junction kept in reverse bias, the current flows through the junction due to minority charge carriers i.e. electrons in P region and holes in N region. The concentration of these current carriers depends on the energy gap E. The saturated value of reverse current Is depends on the temperature of junction diode and is given as :

Log Is = log{A Nn Np(Vn/NpVp/Nn)e –E/kt}

Nn = density of electron in N region

Np = density of holes in P region

Vn = drift velocity of electrons

Vp = drift velocity of holes

K = Boltzmann constant

T = absolute temperature of junction diode

A = area of junction

E = −!slope of line"5.036 eV

EXPERIMENT NO. 9

4. Procedure :

1. First place the diode and the thermometer inside the oven and switch on the oven. 2. Switch off the oven when the temperature reaches 70o. 3. When the temperature becomes steady note the readings of thermometer at a regular

interval of 5o C and corresponding to each value, note the readings of ammeter. 4. Plot the graph by taking log Is on Y-axis and 103. Find the slope of line and then energy

band gap by using the formula.

5. Observation :

Least count of ammeter =

S.NO TEMPERATURE IN OC CURRENT IN A

TEMPERATURE IN KELVIN (T)

103/T Log Is

1

2

3

4

5

6

7

8

9

10

Diode Thermometer

Ammete

r

EXPERIMENT NO. 9

6. Calculation :

/0123 14 0563 = 78 − 79:8 − :9

;63<=> ?@6A =@2 = − B0123 14 05635.036

% error = Standard value − Experimental valueStandard value ∗ 100%

7. Result :

The energy band gap of semiconductor diode = eV

8. Precautions :

1. Maximum temperature should not exceed 70o C.

2. Silicon diode should not be used because it requires a temperature of 125oC. The

thermometer provided will not stand to this temperature. 3. Bulb of the thermometer should be inserted well in the oven.

EXPERIMENT NO. 10

1. Aim :

To determine resolving power of telescope. 2. Apparatus :

Telescope with a rectangle variable slit

A scale with black lines of equal width

meter scale

3. Theory :

According to Rayleigh criterion, two objects of equal intensities are said to be just resolved when in their diffraction pattern, the principal maxima of one coincides with the minima of other. The resolving power of telescope is equal to the reciprocal of that angle subtended at the objective lens of the telescope by the tow far points objects when their image formed in the focal plane of telescope are just resolved. The light ray of wavelength λ from these objects are incident on the objective lens of telescope subtending angle θ after refraction, they form images A & B in its focal plane. From the figure, it is clear that the angular separation between maxima A and B= θ, but from the theory of diffraction at a circular aperture, the angular spread of principal maxima α = 1.22 λ \ d Where, d is the diameter of circular aperture (or the objective of telescope) According to Rayleigh criterion, for just resolution the principal maxima of image of one object must be at the minima of the image of other object. The angular separation between two minima = angular spread of principal maxima. Hence, resolving power of telescope = d \ 1.22 λ If the width of slit mounted on the objective lens is a , when it just resolves the two strips at separation b on the card board (or on the glass plate) kept at a distance D then, the angle subtended by the strips at the slit = b\D = angular separation between the two principal maxima or the angular spread of the principal maxima = λ\a . Hence, just at the limit of resolution. λ \ a = b \ D or λ = ab \ D From equations 1 & 2 resolving power of telescope : RP = Dd \ 1.22ab Knowing all the quantities in the above expression .the resolving power of the telescope can be calculated as :

R. P. = Dd1.22ab radG9

EXPERIMENT NO. 10

d = diameter of the objective of telescope

D = distance of scale from the objective of telescope

a = width of slit mounted on the objective of telescope in the position of just resolution

b = separation between the two strips drawn on scale

4. Procedure :

1. Mount the telescope on the stand with its axis horizontal and scale on another stand. 2. Open the slit completely and focus the telescope on the lines to see their distance

image. Now gradually decrease the width of the slit by the micrometer screw till the separate visibility of the two lines just disappear. Note the reading of micrometer screw in this position.

3. The micrometer screw is rotated in the same direction till the slit is completely closed.

the reading of micrometer screw is again noted. 4. Open the slit gradually till the two lines just appear to be separated from each other

again the reading of micrometer screw is noted. 5. Take mean of two reading of micrometer of just resolution and then take difference of

this value with the shut position. 6. Measure the distance D between slit& scale with the help of measuring tape.

EXPERIMENT NO. 10

5. Observation :

Least count of main scale = 0.05 cm Least count of vernier scale = 0.0005 cm

d = 2.3 cm

b = 0.1 cm

S. no.

Distance between scale & slit D (cm)

Micrometer position of just resolution start while enclosing the slit (A)

When the slit is completely closed (B)

Position of just resolution end while opening the slit (C)

Width of the slit a= A + C2− B MS VS TR MS VS TR MS VS TR

1

2

3

4

MS = Main-scale reading

VS = Vernier-scale reading

TR = Total reading

6. Calculation :

Experimentally : R. P. = Dd1.22ab radG9

Theorotically : R. P. = d1.22λ radG9

% error : % 3<<1< = /J@6A@<A K@0L3 − ;M23<5N36J@0 K@0L3/J@6A@<A K@0L3 ∗ 100 %

EXPERIMENT NO. 10

7. Result :

The theoretical value of resolving power = 31420.76 rad-1 The experimental value of resolving power = Percentage error =

8. Precautions :

1. The axis of telescope must be horizontal. 2. The strips on the scale should be vertical. 3. To avoid the backlash error, the micrometer screw must always be turned in one

direction. 4. The plane of the slit must be parallel to the scale. 5. The width of slit at the position of just resolution must be adjusted carefully.

List of Standard Values

S.No. Quantity Name Standard value

1. Frequency of A.C Mains 50 Hz

2. Wavelength of sodium light 5,890 Å to 5,896 Å

3. Wavelength of green color 4,850 Å to 5,400 Å

4. Wavelength of violate color 3,770 Å to 4,300 Å

5. Band gap for Germanium semiconductor 0.67 eV

6. Grating Element value(Given) 0.002 cm

7. Refractive index of calcite for o-ray 1.658

8. Refractive index of calcite for e-ray 1.486

9. Resolving Power of telescope(given) 31420.7 rad-1