phy lab manual sem-ii

VPCOE, Baramati

Subject Code: (107009)

APPROVED BY: HOD [FE] PRINCIPAL Prof. A. P. Hiwarekar Dr. S. B. Deosarkar

VALIDITY UP TO: ACADEMIC YEAR 2012 – 2013

PRAPARED BY: PROF. ANIL S. DISALE

VPCOE, Baramati

Vidya Pratishthan’s College of Engineering, Baramati

FE Sem-II

List of Experiments

1) Determination of band gap of a semiconductor 2) To study the characteristics of solar cell 3) To study the characteristics of photocell 4) Semiconductor diode characteristics 5) An experiment based on laser

(To find grating element of a given grating using a laser)

FACULTY:

Prof. A. S. Disale Prof. M. G. Lakhe

VPCOE, Baramati

Experiment No :- 01 : Determination of Band Gap of a Semiconductor :

TITLE :

To determine the band gap of a semiconductor. PRIOR CONCEPTS:

Energy bands in solids, conduction band, valence band, forbidden band. NEW CONCEPTS:

Proposition 1: Types of solids Solids can be classified in three groups according to conductivity as- Conductor, semiconductor, insulator. Proposition 2: Forbidden gap Forbidden gap is the gap between top of the valence band and bottom of the conduction band; where no electron is present. Forbidden gap is wide in insulator, narrow in semiconductor and is absent in conductor. Concept Structure: F.B. F.B. 1)Insulator 2)Semiconductor 3) Conductor

Proposition 3: Forbidden Energy: It is the minimum energy required by the electron in valence band to jump

to conduction band.

VPCOE, Baramati. Applied Physics-II

Roll No. -------------

C.B.

V.B. V.B.

C.B.

V.B.

C.B.

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LEARNING OBJECTIVE : Intellectual Skills:

1. To understand difference between forward bias and reverse biasing of diode.

Motor Skills: 1. To make proper reverse bias connections for a given diode. 2. To observe the change in reverse saturation current with change in temperature of diode.

APPARATUS: Thermometer, micro ammeter, battery, semiconductor diode, oven etc.

CIRCUIT DIAGRAM :

PROCEDURE :

1) Make the connections as shown in figure. 2) Insert the thermometer in the hole provided with oven. 3) Now put the power supply ON/OFF switch to ‘ON’ position and

see that the jewel light is glowing. 4) Put the ‘OVEN’ switch to “ON’ position and allow the oven

temperature to increase up to 70 0C. 5) As soon as the temperature reaches 70 0C switch off the oven. 6) Take the readings during the fall of temperature from70 0C in step

of 5 0C up to room temperature.

Thermometer

µA

◄ +

_ D C Supply

Oven

+ _

P N

- +

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7) Tabulate your readings in the form as shown in the observation table.

8) Plot the graph between log I vs 1 / T K, the nature of graph is straight line.

9) Find the slop and calculate band gap Eg = 2kβ.

OBSERVATION TABLE :

Sr. No.

Temp T 0C

Temp T K

1/T K

Current I (µA)

Log10

(I)

01 70

02 65

03 60

04 55

05 50

06 45

07 40

GRAPH:

Find Slope (β)

1 / T K

Log10 (I)

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SAMPLE CALCULATIONS :- Band gap of a given semiconductor

Eg = 2kβ where β = m = Slope of graph and k = Boltzmann constant = 8.63 x 10 – 5 eV/K Eg = ---------------------- eV

QUESTIONS: 1. State the reason why energy band are formed in solid instead of energy

loses. 2. How are the band structure of insulator and semiconductor similar?

How are they different? 3. State the reason that can cause a solid to be metal (conductor) with

respect to band structure. 4. The forbidden energy gap for silicon is 1.1eV and for germanium is

0.7eV which of the above material will have more conductivity? Why? 5. Define reverse saturation current (Is). How it depends on change in

temperature. 6. If the germanium is doped with arsenic, is the result n-type or p-type

semiconductor? Why? 7. How band structure is useful in classifying the solid according to its

conductivity.

Result :-

Forbidden energy gap for germanium diode = ------------eV.

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Experiment No :- 02 : Study of Solar Cell Characteristics:

TITLE:

To find out the fill factor of given solar cell. PRIOR CONCEPTS: Basics of Solar cell, basics of electric circuit, concept of electric power NEW CONCEPTS: Proposition1: Photovoltaic effect: Light can be converted in to electrical energy if a pn junction is used. Proposition2: Fill Factor Fill factor is the ratio of actual maximum obtainable power (Vm X Im) to the theoretical (not actually obtainable) power. LEARNING OBJECTIVES:

Intellectual Skills: 1. To identify different circuit components. 2. To interpret the graph of current verses voltage for solar cell. Motor Skills: 1. To make the connections as per the circuit diagram. 2. To take and tabulate observations carefully. 3. To plot the graph for characteristics of solar cell APPRATUS: Solar cell circuit, voltmeter, microammeter, digital multimeter etc. CIRCUIT DIAGRAM:


Roll No. -------------

+ µA + -

-

V RL

+

-

Solar

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PROCEDURE:

10) Connect the circuit as shown in diagram.

11) Switch on the lamp.

3) Use digital multimeter as voltmeter and micro ammeter for measuring

current.

4) Measure short circuit current (ISC) for zero load (i.e. RL = 0)

5) Measure open circuit voltage (VOC) when RL is maximum.

6) Now make RL = 0, vary RL and note corresponding values of voltage and

current.

7) Plot I-V curve.

8) Draw a line making an angle 450 with X-axis to meet the curve at a

point, find it’s co-ordinate Im and Vm gives maximum power dissipation.

9) Calculate fill factor ‘FF’.

OBSERVATION TABLE :

Sr. No.

V

I (µA)

01 0.0 --- (Isc)

02 0.5 ---

03 1.0 ---

04 1.5 ---

--- --- ---

--- --- (Voc) ---

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GRAPH:

OBSERVATIONS (FROM GRAPH) :

1) Short circuit current Isc = ---------- µA

2) Open circuit voltage Voc = ---------- V 3) Maximum current Im = ---------- µA 4) Maximum voltage Vm = ---------- V

CALCULATIONS : Fill factor of a given solar cell (FF) = Im Vm

—————— x 100 ISC VOC

FF = ………%

Result :- Fill factor of a given solar cell = ---------- %

Vm Voc

Im

Isc

450

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QUESTIONS:

1. What is solar cell? 2. What is photovoltaic effect? 3. Explain the difference between photovoltaic effect and photoelectric

effect? 4. What are the advantages of solar cell? 5. Which materials are used for manufacturing of solar cell ? 6. Compare: production of electricity through solar cell and through

conventional energy source.

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Experiment No :- 03 : Characteristics of a Photo Cell:

TITLE: To study characteristics of Photo Cell. PRIOR CONCEPTS: Photoelectric effect, electromagnetic radiation, dual nature of light.

NEW CONCEPTS:

Proposition1: Photosensitive material: Material that exhibit photoelectric effect is called photosensitive material.

e.g. Ag – O – Cs, Sb – Cs, Bi – Ag – O – Cs

Proposition 2: Characteristics of photoelectric effect: Emission of photocurrent is instantaneous; the photocurrent is directly proportional to the intensity of the incident light.

Proposition 3: Devleopment of QM It is a key experiment in the development of quantum mechanics.

LEARNING OBJECTIVES:

Intellectual Skills: 1. To identify different circuit components 2. To interpret the graph plotted I Vs V for photoelectric effect.

Motor Skills: 1. To make the connections as per the circuit diagram. 2. To take and tabulate the observation carefully. 3. To plot the graph.

APPRATUS: Voltmeter, Micro ammeter, 100 W bulb, Photo cell etc.

Circuit Dia gram :-


Roll No. -------------

- +

+

µA

- V

A

C

+

-

Key

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PROCEDURE:

1) Make the connections as shown in the figure. 2) Switch on the light unit, the light intensity can be varied with the help

of pointer provided. 3) Allow the light to fall on photocell. 4) Switch on the apparatus. 5) Now increase the voltage in the steps of 5V and take the corresponding

readings of current from micro ammeter. 6) The procedure is repeated for different light intensities. 7) Plot the graph for photocurrent Vs voltage. OBSERVATION TABLE: GRAPH:

High Intensity

Low Intensity

Sr. No.

V I (µA) V I (µA) 01 5 5 02 10 10 03 15 15 04 20 20 05 25 25 06 30 30 07 35 35 08 40 40 09 45 45

I

V

High Intensity Low Intensity

RESULT: Law of photoelectric effect is verified (photoelectric current is directly proportional to the intensity of incident radiation).

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QUESTIONS:

1. What is photoelectric effect? 2. What is conclusion of this experiment? 3. Light of wavelength 2000 Å falls in an aluminum surface with work

function 4.2 eV calculate i) Threshold wavelength ii) stopping potential

4. Is it possible to liberate an electron from a metal surface having work

function 4.8eV with an incident radiation of wavelength i) 5000 Å ii)2000 Å

5. The photoelectric work function of potassium is 2.0 eV . If light

having wavelength 3600 Å falls on potassium ,find

i) Stopping potential ii) Kinetic energy in eV of most of the energetic electrons ejected

and velocities of these electrons

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Experiment No :- 04 : Semiconductor Diode & Zener Diode Characteristics:

TITLE:

To plot I-V characteristics of a semiconductor diode and zener diode and to determine knee voltage and zener break down voltage. PRIOR CONCEPTS: P-type and N-type semiconductor, P-N junction, Zener diode. NEW CONCEPTS: Proposition 1: I-V characteristics of P-N junction. It is the graph plotted forward current verses forward voltage and reverse current verses reverse voltage.

Proposition 2: Forward bias characteristics In forward bias initially the forward current increases gradually with applied forward voltage, after knee voltage forward current increases suddenly with small change in the forward voltage. Proposition 3: Reverse bias characteristics In reverse bias characteristics reverse current increases by small amount with reverse voltage. Proposition 4: Zener breakdown voltage The zener breakdown occurs when the electric filed across the junction, produced due to reverse voltage is high .It causes an increase in number of free carries hence an increase in current. LEARNING OBJECTIVES :

Intellectual Skills :

1. To understand the forward bias and reverse bias circuit for P-N junction /zener diode.

2. To interpret the graph plotted I vs V in forward and reverse bias circuit

Motor Skills: 1. To make connections as per circuit diagram. 2. To make and tabulate the observations carefully. 3. To plot the graph for the forward and reverse bias.


Roll No. -------------

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APPRATUS: Board fitted with the semiconductor diode, zener diode and dc variable power supply, milliammeter, and voltmeter.

CIRCUIT DIAGRAM:

PROCEDURE :

I) Forward bias semiconductor diode and zener diode: 1) Connect the given diode in forward bias. 2) Connect milliammeter in series and voltmeter in parallel. 3) For various values of voltage, note the corresponding values of the current by varying the power supply. 4) Plot current I verses voltage V characteristics. 5) Determine cut-in voltage for given diode.

II) Reverse biasing semiconductor diode and zener diode: 1) Connect the given diode in reverse bias. 2) Connect micro-ammeter in series and voltmeter in parallel for

Semiconductor diode. 3) For various values of voltage note the corresponding values of the

current by varying the power supply. 4) Plot current I verses voltage V characteristics. 5) Connect milliammeter in series and voltmeter in parallel for zener

Forward Bias

+

- V

+

-

mA + -

+- ▼▼ ▲

+

- V

+

-

+ -

+

-

mA

Reverse Bias

▲

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diode. 6) For various values of voltage note the corresponding values of the

current by varying the power supply. 7) Plot current I verses voltage V characteristics. 8) Determine breakdown voltage for zener diode.

OBSERVATION TABLE: I) Germanium Diode

II) Zener Diode

Forward Biased

Reverse Biased

Sr. No.

V I (mA) V I (µA) 01 0.1 1 02 0.2 2 03 0.3 3 --- --- --- --- --- --- --- --- ---

Forward Biased

Reverse Biased

Sr. No.

V I (mA) V I (mA) 01 0.1 1 02 0.2 2 03 0.3 3 --- --- --- --- --- --- --- --- ---

RESULT :- 1) For Germanium diode cut-in voltage is = -------- V 2) For zener diode cut-in voltage is = -------- V 3) For zener diode break down voltage is = -------- V

Forward Bias

Cut in voltage

Reverse Bias

I

V

Break down voltage

Forward Bias

Cut in voltage

Reverse Bias

I

V

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QUESTIONS:

1. What is the value of barrier potential for silicon and germanium? 2 Explain the formation of potential barrier across the junction region of semiconductor. 3. What is a zener diode? Draw the equivalent circuit of an ideal zener in breakdown region. 4. Explain application of zener diode as voltage regulator. 5. Discuss some of the applications of pn junction diode.

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Experiment No :- 05 : An Experiment based on Laser:

TITLE:

To determine the Grating element of given plane diffraction grating using diode laser.

PRIOR CONCEPTS: Characteristics of laser, diffraction of light, diffraction grating.

NEW CONCEPTS: Proposition 1: Semiconductor laser:

A semiconductor diode laser is specially fabricated pn junction device that emits coherent

light when it is forward biased.

Proposition 2: Grating element The spacing between adjacent slits is known as grating element.

LEARNING OBJECTIVE:

Intellectual Skills: 1. To observe diffraction pattern of different order. 2. To draw the conclusions form observation and relates them to propositions.

Motor Skills: 1. To arrange the set up for the experiment. 2. To draw ray diagram for the experimental setup 3. To observe the phenomenon of diffraction of light and measure correct value of angle of diffraction. APPRATUS: Diode laser, diffraction grating, stand, screen, etc.

VPCOE, Baramati. Applied Physics-II Roll No. -------------

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RAY DIAGRAM:

PROCEDURE:-

1) Fit the diode laser on stand. 2) Keep the grating in front of laser, make laser on and focus it on grating to from the well diffraction pattern on the screen. 3) Identify the central maximum and different order of spectrum on either side of central maximum. 4) Measure the distance of first order spectrum from the central maximum on either side. 5) Measure the distance between diffraction grating and the screen(x) 5) Repeat the measurements for different order of spectrums and tabulate the readings.

OBSERVATIONS:

1) Wavelength of Laser diode = 6290 Å

2) Distance between diffraction grating and screen ( x ) = ---------------

Screen

LASER

Diffraction Grating

n=1

n=1

) θ ) θ

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OBSERVATION TABLE:

Distance from central Maximum Sr.

No.

Order of spectrum

(n) Upper side (y1) cm

Lower side (y2) cm

y = (y1+ y2) / 2 cm

Diffraction angle

=tan-1(y/x)

01

1

02

2

SAMPLE CALCULATIONS: - Formula for wavelength:

d sinθ = nλ Where ‘d’ is grating element

and ‘n’ is order of spectrum Grating element (d) = nλ / sinθ

d = --------------------------------------- cm

QUESTIONS:

1. Write the acronym use for ‘LASER’

2. Name the types of lasers on the basis of material used for it.

3. Mention three characteristics of laser in detail.

4. How laser is different from ordinary source of light?

5. Explain working of semiconductor laser.

6. State applications of laser in information technology.

7. Calculate the power per unit delivered by laser pulse of energy 4.0 X 10-3 J and pulse

length of 10-9 sec .When pulse is focused on small spot of radius 1.5 X 10-5 m.

RESULT:- Grating element of given plane diffraction grating, d = ----------- cm

phy lab manual sem-ii

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