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LMPHY-122 PHYSICS LAB-II

PHYSICS LABMANUAL

Course Code: PHY122Course Title: PHYSICS LAB-II

The principle of science, the definition, almost, is the following: The test of all

knowledge is experiment. Experiment is the sole judge of scientific “truth.” But what is the source of knowledge? Where do the laws that are to be tested come from?

Experiment, itself, helps to produce these laws, in the sense that it gives us hints. But

also needed is imagination to create from these hints the great generalizations-to guess

at the wonderful, simple, but very strange patterns beneath them all. And then to

experiment to check again whether we have made the right guess.

Richard Feynman




SR.NO.

DESCRIPTION

1 An introduction to units, errors ,different types of graphs and measurement of length, massand time

2 To study the induced e.m.f as the function of velocity of magnet.

3 To study the variation of magnetic field with the distance along the axis of circular coilcarrying current by plotting a graph.

4 To find the frequency of ac main by using electric vibrator.

5 To plot a graph between current and frequency in series and parallel LCR circuit and findresonant frequency, quality factor and band width.

6 To study the voltage regulation and ripple factor of (a) Half Wave Rectifier (b) Full WaveRectifier (c) Bridge rectifier and trace it input and output . Also study the L-type and π-typefilter circuit.

7 To find the coefficient of self inductance of a coil by Anderson’s method using a head phone.

8 To determine Hall Voltage and Hall Coefficient using Hall Effect.

9 To study the characteristics of PNP and NPN transistor (CE and CB).

10 To trace the Lissajous figures using CRO. Also find the phase shift.

11 To find the wavelength of He-Ne laser by using Michelson interferometer.

12 To study the output characteristics of FET/MOSFET

13 To measure the capacitance of plate capacitor by charge measurement/ as a function ofarea of plates/determine the dielectric constant of different materials

14 To draw the forward and reverse characteristics of P-N junction diode and draw load line.

TEXTBOOK:1. LMPHY122.doc

OTHER READINGS:2. Arora C.L., ” B.Sc. Practical Physics” Chand S. & Company, New Delhi,

Twentieth edition, 2007




Experiment 1Title: Simple measurements and graphical analysis

Equipment to used: Vernier callipers, screw gauge and multimeter

Material Required: Linear-linear and semi-log graph paper

Learning objective: (1) Students learn the use of Vernier caliper, screw gauge andmultimeter

(ii) Students learn to plot linear-linear and semi-log graphsIntroduction: The precision of length measurements may be increased by using a device

that uses a sliding vernier scale. Two such instruments (identify in the picture above) thatare based on a vernier scale which you will use in the laboratory to measure lengths of objects are the vernier callipers and the micrometer screw gauge. These instruments

have a main scale (in millimetres) and a sliding or rotating vernier scale.A multimeter is an electronic measuring instrument that combines several measurement

functions in one unit. A typical multimeter may include features such as the ability tomeasure (AC/DC) voltage & current, resistance and testing of a diode.

Zero error occurs when the measuring instrument registered a reading when thereshould be none.

Least count of a measuring instrument is the smallest quantity that can be measuredaccurately using that instrument. The degree of accuracy of a measurement can be

concluded from the least count of the instrumentProcedure:

Part A (Measurement)

1. To find the density of the given material

You are given a rectangular block and you have to find the density of material of whichthe rectangular block is made of. We know density(d) =[mass(m kg)/volume (V m

3)].

To find the volume of the rectangular block measure its length, width and height byvernierc caliper.

Take at least five readings of each dimension. Also remember to check and note in

your “report sheet” the zero error and least count of the vernier caliper you are

using. Even if “zero error” is “zero” entry should be recorded in your report sheet.

Next measure the mass of the rectangular block using a balance; take at least fivereadings. Also note “zero error” and “ least count” of the balance you use for finding themass.

Tabulate the data, calculate the density along with the possible error.

Error in density( d)

d=m/V or d/d= (m/m)+ (V/V) ( derive this expression)

Estimate (m) and (V) to estimate the error (d) in the density you have found out inyour experiment.




2. To find the resistivity of a given metal wireYou will need screw gauge and a multimeter for this experiment.

Resistivity (=Resistance(R ohms) [ area of cross-section of the wire (A m

2)/ length of the wire(l m)]

Derive the units of

Take a piece of a metal wire of almost uniform cross-section; measure (at leat five times)its cross section by screw gauge and length (at least five times) by vernier caliper.

Measure the resistance of the above piece of wire using a multimeter( at leat five times)

Tabulate the data and calculate along with possible errors.

Error in

= R A/l so that RRAAll

How do you estimate A?

Part B (graphical analysis)

Linear graph paper

Let us consider the case of time period „T‟ of a simple pendulum which is written as

T = (2) (L/g)1/2

----------(1)„L‟ is the “length” of the pendulum while „g‟ is acceleration due to gravity. Eq. (1) can berewritten as

T2

= (42 /g) L---------(2)

Eq. (2) is an equation of straight line with slope = (42/g) and intercept = 0One can find the value of “g” from the graph of T

2with L.

In one of the experiments on simple pendulum a student came up with the following data

Table 1

S. No Time for 10 oscillations(s)

Effective length of the pendulum(m)

1 16 0.6

2 18 0.83 20 1.0

4 22 1,2

5 24 1,4

6 25 1.6

7 27 1.8

8 28 2.0

Find the value of “g” by plotting the above data i.e T2

Vs L; T is the time period of the

pendulum for its effective length L.

How to plot the graph

Step 1. From Eq. 2 we have to plot T2

vs L (L should in meter)Prepare the Table with following headings ( prepare directly in your Lab Report Sheet)

Sample Table

S.No. L

(m)

T

(s)

T2

1. 0.6 1.6 2.56~2.6




Step 2. Choose a “linear” graph sheet which is linearly (normally in mm) graduated onboth X as well Y- axis

Step 3. Choose Y-axis for T2

and X-axis for LStep 4. Max T2 is 1 and min is 0.25; choose your scale so that you can mark 0.25 clearly.

Similarly choose scale for L on X-axis.

Step 5. Mark the points on the graph with a sharp pencilStep 6. Draw a straight line through the points so that maximum number of points arevery close to the line (Best fit we will not discuss presently)

Step 7. Find the slope from the graph and calculate “g”

Exercise

In the above experiment the error ( in time period T is (0.1s) while the length L has

error (L) equal to 0.01m. Calculate the error in “g”

Semi-log graph paper

Radioactive decay is given by N(t) = N(0) e-at , where N(t) are the observed counts attime t,

N(0) are the counts at time t = 0 (fixed arbitrarily) and a is the decay constant. Calculate

N(0)and a by graphical technique from the given data (Table 2)

N(t) = N(0) e-at

Or ln N(t) = ln N(0) - t (ln is log to the base e)

Or 2.3log N(t) = 2.3 log N (0) -t (change of log base to 10)

Or log N(t) = log N(0) - ( /2.3) t……………….(3)

This is an equation of a straight line with y=log N(t), x- - ( /2.3) t with log N(0) as

intercept and plot of log N(t) vs t will give values of “” . Since y is in log form and x isin linear form the plot has to to prepared using “semi-log” graph paper whose y-axis is inlog scale while x-axis is in linear scale.

Table 2 summarizes the data collected from an experiment on radioactive decay. Plot the

data on semi-log paper and calculate “” and N(0) for this decay.

Exercise: Half-life “ ’ is defined as the time needed to have [N(t)/N(0)]= ½; derive an

expression for “ ”.

Calculate the value of “” for the radioactive process tabulated in Table 2.

Table 2

Time (days) Relative Activity

0.2 35.0

2.2 25.0

4.0 22.1

5.0 17.9




6.0 16.8

8.0 13.7

11.0 12.4

12.0 10.3

15.0 7.5

18.0 4.9

26.0 4.0

33.0 2.4

39.0 1.4

45.0 1.1

Important:

(i) Give a title to the graph; in present case it will be T2 Vs L for a simple pendulum.

(ii) Mark scales on the graph sheet; X-axis “10mm = so many m” and Y -axis “10mm=

so

many seconds”

(iii) Mark X-axis and Y-axis with quantity (along with units) you are plotting

(iv)Calculate the slope and “g” on the graph sheet so that a graph is complete and one

need not to refer to the Lab Sheets.

Interpolation: From the graph you can find the L for T=0.44 (for example, within the

present data set)) even though there is no experimental data; this process is called

interpolation. Extrapolation: One can extend the length of the line so that one can predict L for T

=0.1s or 2.5s (outside the present data set); this is called extrapolation.




Example 2. Change in the value “g” with the distance “h” (outside the earth) is given

by g h (value of g at a height h)= g(1-2h/R) where R is the radius of earth

Data from an experiment is given in the following tableS.No gh

m/s2

hm

1 8.8 0.05R

2 7.8 0.10R

3 6.9 0.15R

4 5.9 0.20R

5 4.9 0.25R

6 3.9 0.30R

By graphical analysis find the value of “g”. Can you find out the value of “R” from the

graph?Semi-log graph

Radioactive decay is given by N(t) = N(0) e-t

, where N(t) are the observed counts at

time t, N(0) are the counts at time t = 0 (fixed arbitrarily) and is the decay constant.

Calculate N(0) and by graphical technique from the given data:

Time „t‟

S

No. of counts

1.0 905.0

2.0 820.0

3.0 735.0

4.0 670.05.0 600.0

6.0 550.0

N(t) = N(0) e-t

Or ln N(t) = ln N(o) - t (ln is log to the base e)

Or 2.3log N(t) = 2.3 log N (0) -t (change of log base to 10)

Or log N(t) = log N(0) - ( /2.3) t

Plot of log N(t) with t is a straight line with log N(o) as intercept and -2.3 as slope.

Since one side is log so use a semi-log graph paper to get the values of N(0) and

Log-log graphPlanetary period „T‟ (in earth years) is related to its distance „R‟( AU, astronomicalunits; 1AU is equal to average separation between earth and sun) by the relationship of

the formT = kR

n

Calculate ‘k’ and ‘n’ by graphical analysis from the following data




T = kRn

or log T = log k + n log RPlot of log T vs log R is a straight line with log k as intercept and n as slope. Since both

sides are in log form use log-log graph paper.

Error analysis

Measurement is basic to science. A measurement is meaningful only if the uncertaintiesinvolved are specified. An operator “X” has to specify the uncertainty (error) in his final

result; the practice of

comparing the result with“standard value” isunscientific as the

experimental

conditions/instruments used to find out the “standard value” are different when compared

to those of X. Please remember

The error in an experimentally measured quantity is never found by comparingit to some number found in a book or web page

These uncertainties do not include the blunders/mistakes of the person performing the

measurement. These errors are due to limitations of the measuring instruments (like zeroerror, faulty calibration, error due to parallax, bias of the operator etc) and uncontrollable

changes in experimental parameters like temperature, pressure, voltage etc. Theinstrument errors (systematic errors) are instrument specific, can be either +ve or – ve and

Name of the planet T inEarth years

R inAstronomical units

Mercury 0.39 0.24

Venus 0.72 0.62

Earth 1.00 1.00

Mars 1.52 1.88

Jupiter 5.20 11.86

Saturan 9.54 29.46




are constant in nature. On the other hand errors due to changes in experimentalparameters are random in nature; can be both +ve as well as – ve in a particular set of

easements.

Estimation of systematic errors

There is no prescribed method to minimize systematic errors. An operator has to examine

various measuring instruments (scales, meters, etc) for zero-errors (zero of a meter orvernier caliper might have shifted), take readings so as to minimize parallax error and if possible check the calibration of the measuring instruments. Systematic errors cannot be

minimized by taking large number of measurement (Why?).

Estimation of random errors

Random errors are both +ve as well – ve in a measurement cycle, can be handled by well-known statistical techniques. Two basic techniques are:

(i) Arithmetic Mean or simply mean = (X1 + X2 + X3+…………………………..+XN)/N=XM

(ii) Standard deviation = (1/N) [(X1-XM)2

+ (X2-XM)2

+ (X3-XM)2 +………..+(XN-

XM)2

1/2

It shows how much deviation there is from the "average" (mean). A low standarddeviation indicates that the data points tend to be very close to the mean. whereas high

standard deviation indicates that the data are spread out over a large range of values.

Propagation of random errors

If Z is a function of X and Y so that we have Z = F(X,Y). Error in X is X while for Y

the error is Y how to find error in Z ( Z) X and Y are independent that measurementin X does not induce error in Y and vice versa; this is the case in most of your

experiments.)

What will be Z in case Z = X – Y ? The standard procedure is:

Contribution to the error Z due to X is given by (F/ X) X [(F/ X) is partial

derivative of F with respect to X treating Y as constant) while due to Y the contribution

is (F/ Y) Y.

Total Z is given by

Z = (F/ X)2

(X)2

+(F/ Y)2

(Y)2

(1/2)

Example1. Z= X+Y

Z/ X =1, Z/ Y = 1 so Z = ( X)2

+ ( Y)2

(1/2)

What will be Z in case Z = X – Y ? What conclusion you arrive at from this example?

What will be Z in case Z =a X + Y/b ? where a and b are constants?

Example2. Z = XY

Z/ X =Y, Z/ Y = X Z = Y 2( X)

2+X

2( Y)

2

(1/2). This is absolute error in Z.

Alternately we can have Z/Z = Z/XY =( X/X)

2

+ ( Y/Y)

2

(1/2)

. This is relative error inZ and can be expressed in terms of % by the relation ( Z/Z) x 100.

Example3. Z = X/Y

Z/ X = 1/Y, Z/ Y = -X/Y 2 Z =(1/Y)

2( X)

2+[(X)

2]/Y

4( Y)

2

(1/2).

Which gives Z/Z =( X/X)2 + ( Y/Y)2 (1/2).

The procedure outlined above can be used for functions with more than two independent

variables.




Significant figures

The final result of an experiment should be expressed [measured value] ± [estimatederror] units. If it is a single measurement like measurement of length your final result

could be for example, 10.28±0.05cm which means that the length could be from 10.33 to

10.23cm. All the four digits in the result are important; your result has four significantdigits. If the object whose length was measured has breadth say 5.41±0.05cm (measuredwith the same scale used for the measurement of length so that error is same). Area =

(10.28±0.05cm) x (5.41±0.05cm). (10.28) x (5.41) = 55.6148 and error in area =(0.05)

2+ (0.5)

2

1/2= 0.070710678 (calculated on CASIO 5-VPAM). So our result will

look like 55.6148±0.070710678 cm2. We know the error in our length as well as breadth

measurement is 0.05cm so the order of magnitude of the error in area must be same

which turns out to be 0.07cm when you carefully examine the final result for area. Note

that the error in area is more than that of length or breadth which is expected(WHY?). So

area = 55.6148±0.07cm2

which means that area is expressed to 1/10000 accuracy whileerror is only accurate to 1/100. Hence digits 4 and 8 have no significance in the final

result which is area = 55.61±0.07 cm2

.

Errors in the measurement determine the number of significant digits one should use in the final result

How to calculate errors in your Lab experiments1. Check for zero-errors in all your measuring instruments like scales, vernier calipers,

screw gauges, volt/amper meters etc and note them properly in your “LAB Note Book”=no rough copy is to used in the LAB for recording of the data.

2. Check and record the least count of all the measuring instruments. Examine eachinstrument carefully to determine the least count. For example a scale may be graduated

so that it has “markers‟ after every one mm; least count being 0.1cm. However, if the

“markers‟ are distant enough so that one can read to an accuracy of o.5mm the least countis 0.05cm.

Intelligent and careful use of the measuring instruments to get best out of these

instruments is the basic experimental skill. In real world you will never get

ideal instruments.3. Make the required measurements and record these measurements directly in your“LAB note book”. Units of all the quantities you have entered in the note book should be

mentioned.

4. Compute the result

5. Calculate the error by standard deviation technique.

6. Calculate the percentage error by “partial differentiation technique”




Experiment No.2: To Study the induced e.m.f. as function velocity of the magnet.

Equipment Required: A small permanent magnet mounted at the middle of a semi-circular

arc, a coil consisting of number of turns, two weights, stopwatch, capacitor, diode, resistance,

voltmeter

Material Required: A small strong permanent magnet, a stopwatchLearning Objectives:

Electromagnetic induction

Induced e.m.f

Dependence of the magnitude of induced e.m.f on the velocity of the magnet.

Outline of the Procedure:

Mount the magnet at the middle point of the semi-circular arc and suspend the rigid

aluminium frame from its centre so that whole frame can oscillate freely through the

coil.

Adjust the position of two weights on the diameter arm of the arc to have minimum

time period.

Connect the terminals of the coil to the diode circuit for measuring the peak value of

induced e.m.f.

Note time for about 20 oscillations with an amplitude of about say 20cm and

respective peak voltage.

Repeat thrice keeping the amplitude same and find the time period. Also note the peak

voltage each time.

Repeat the experiment after changing the amplitude and take 8-10 readings.

Now change the time period by adjusting the position of the weights on the diameter

arm. Take about three readings at this position.

Repeat the experiment after changing the time-period and take 8-10 readings.




Scope of the results expected: This experiment will help in understanding the nature and

polarity of induced e.m.f. One can apply the acquired knowledge to see the dependence of

induced e.m.f. on velocity of magnet w.r.t. the pickup coil.

Parameters and Plots:

(A) Time period constant, amplitude variable:

Mean position of the centre of the magnet= cm.

Radius of the semi-circular arc R0= cm.

Sr.No. Amplitude

a = R0Ɵ0

Time for 20

Oscillations

Mean time

period(T)

eo eo /a= eo / R0Ɵ0 Linear velocity

v = (2Π/T) R 0Ɵ0

1

.

.

.

(i)

(ii)

(iii)

Mean

2

(B) Amplitude constant, time period variable:

Sr.No. Amplitude

a = R0Ɵ0

Time for 20

Oscillations

Mean time

period(T)

eo eoT Linear velocity

v = (2Π/T) R0Ɵ0

1 (i)

(ii)

(iii)

Mean

Model Plot:




Cautions:

The semi circular frame should oscillate freely as a whole on the knife edge.

The magnet should pass freely through the coils..

The magnet should be small and should be mounted at the middle of the semi circular

arc.




Experiment No. 3

Title: To study the variation of magnetic field with the distance along the axis of circular coil

carrying current by plotting a graph. (Using Stewart and Gee‟s apparatus.)

Equipments required: Stewart and Gee‟s type tangent galvanometer, a battery, a rheostat, an

ammeter, a one-way key, a reversing key, connecting wires.Material Used: NA

Learning Objectives:

To understand the working of Tangent Galvanometer using Tangent Law. To study the direction and magnitude of the magnetic field around the coil.

Circuit Diagram

Outline of Procedure:

1. Place the instrument in such a way that the arms of the magnetometer lie roughly east and

west and the magnetic needle lies at the centre of the vertical coil. Place the eye a littleabove the coil and rotate the instrument in the horizontal plane till the coil, the needle and

its image in the mirror provided at the base of the compass box, all lie in same verticalplane. The coil is thus set roughly in the magnetic meridian. Rotate the compass box so

that the pointer lies on the 0-0 line.2. Connect the galvanometer to a battery, rheostat, one way key and an ammeter through a

reversing key.3. Adjust the value of the current so that the magnetometer gives a deflection of the order of

60-700 degrees. Reverse the current and note the deflection again.4. Now slide the magnetometer along the axis and find the position where the maximum

deflection is obtained.5. Note the position of arm against the reference mark and also the value of current. Read

both ends of the pointer in the magnetometer, reverse the current and again read bothends. Now shift the magnetometer by 2 cm and note the reading again. Record a number

of observations.




6. Similarly repeat the observation by shifting the magnetometer in the opposite directionand keeping the current constant at the same value.

Observations.

Least count of the magnetometer =

Current I =

S. No Distance from

the centre,x

(in )

Left Side Mean θ tan θ Right Side Mean θ

Direct Reversed Direct Reversed

Scope of the result to be reportedPlots & Parameters: Plot a graph between tan θ and x, where θ is the deflection produced in

a deflection magnetometer and „x‟ is the distance from the centre of the coil. The intensity of magnetic field varies with distance from the centre of coil, the

graph can be plotted and variation can be known. The intensity of magnetic field is maximumat the centre and goes on decreasing as we move away from the centre of the coil towards

right or left.The value of magnetic field at the centre of coil and radius of coil can also be

determined from this experiment. A graph showing the relation between B and the distance

„x‟ is plotted. The curve is first concave towards O and then afterwards becomes convex.

Then the points where the curve changes its nature are called the point of inflection. Thedistance between the two points of inflexion is equal to the radius of the circular coil.

Cautions: 1. There should be no magnet, magnetic substances and current carrying conductor near the

apparatus. 2. The plane of the coil should be set in the magnetic medium.

3. The current should remain constant and should be reversed for each observation.




Experiment4: To find the frequency of a.c. mains using electrical viberator.Equipment Required: Electric vibrator, A.C supply source, a table clamp along with

frictionless pulley, weight pan, weight box

Material required: a long uniform thread

Learning objectives:

(i) To find the frequency of a.c. mains

(ii) To verify the law of string

Diagram:

Outline of the procedure:

1. The current is switched on and the length of the steel rod is adjusted such that the free

end of the rod starts vibrating with maximum amplitude.

2. The current is then switched of and a string of about 2m length is tied to the free end

of the rod and the other end of the rod is passed over a frictionless pulley fixed onthe table. To this end a light weight pan is attached and some weights are added on it

to make the string taut.

3. The current is again switched on and the string starts vibrating. The length of the

string is adjusted by moving the vibrator forwardor backward to get sharp loops and clearly marked nodes.

4. The positions of the extreme loops are marked leaving the first and and the last loop.5. The distance between the two marks is measured and then divided by number of

loops to get the length of one loop.

6. The experiment is repeated three times by taking three different weights in the pan.

Scope of the results expected:




Actual frequency of a.c. mains is 50Hz.

Parameter and Plots:

Frequency of a.c. mains(n) = frequency of the vibratorTherefore,

where m is the mass per unit length of the string, l is the length of one loop and T is the

tension produced in the string which is given by

T = weight of pan + weight in pan

= (mass of pan + mass in pan)g

g = 980 cm/s2

Therefore, for different values of T, find the corresponding values of n.

Report data in tabular form.

Caution:

1) Make sure that the string should be of uniform thickness and free from knots

2) Nodes and antinodes should be sharply defined.3) The pulley should be frictionless.




Experiment No. 5- To plot a graph between current and frequency in LCR series and parallel

circuit and find resonant frequency, quality factor and band width.

Equipment Required- An audio-frequency oscillator (range 10 Hz to 10 kHz), an inductance

coil, variable capacitors, variable resistors, a non-inductive resistance box, ac milliammeter,ac voltmeter, connecting wires etc.

Material Required: NA

Learning Objective - To experimentally study LCR series and parallel circuit.

2. To find the quality factor and resonant frequency.

3. Also calculate bandwidth from the graph.

4. Be able to explain why LCR series circuit is called acceptor and LCR parallel circuit iscalled rejector circuit.

Circuit diagram:

Fig: Series LCR Circuit Fig: Parallel LCR Circuit

Procedure: 1. Connect the LCR (series/parallel) circuit.

2. With output voltage of the oscillator kept constant throughout the experiment vary thevalue of A.F. and measure the corresponding value of current in millammeter for each

observation.

3. Repeat the experiment for two more different values of R.




4. Plot a graph between current (y axis) and frequency (x axis).

Observations:

Resistance R =

Capacitance C =Inductance L =Output voltage of audio oscillator = Input voltage for LCR Circuit , Ev =

S. No Frequency (in ) Current in the circuit (in mA) for

R1 R2 R3

Current at resonance from the graph for

(i) R1 =(ii) R2 =(iii) R3 =

Calculated value of current at resonance for(i) R1 = Ev /R1

(ii) R2 = Ev /R2

(iii) R3 = EV /R3

Resonant frequency, νr = 1/(2π LC )

Resonant frequency, νr (graphically) =

Quality FactorMaximum value of current at resonance Ir =

Corresponding Frequency νr =0.707 Ir =

Corresponding value of frequency

below νr , ν1 =

above νr, ν2 =Band Width = ν2 - ν1 =

Quality Factor, Q = 2π

12

r

Calculated value of Q from inductance L = (ωrL)/R = R

Lr

2

Calculated value of Q from inductance L = R

C r ) / 1(

=r

CR 2

1

Parallel Circuit

S. No Frequency (in ) Current in the circuit (in mA) for

R1 R2 R3

Current at (anti) resonance from the graph for




(i) R1 =C R

L

1

=

(ii) R2 =C R

L

2

=

Impedance at resonance Z =Calculated value of current at (anti) resonance for

(i) R1 = Ev /Z = L

C R E v 1

(ii) R2 = Ev /Z = L

C R E v 2

Anti Resonant frequency, νr (graphically) =

Calculated value for R1 =2

1

2

2

11

L

R

LC

Calculated value for R2 =2

1

2

2

21

L

R

LC

Plots and parameters:Current vs. frequency

Scope of the Result-

Graph between current and frequency will be Gaussian.

Resonant frequency, quality factor and band width can be calculated from the graph.Cautions-

If the amplitude of the output voltage of the oscillator changes with frequency, it

must be adjusted.

The values of inductance and capacitance are so selected that the natural frequency

of the circuit lies almost in the middle of the available frequency range.




Experiment No. 6: To study the voltage regulation and ripple factor of (a) Half Wave

Rectifier (b) Full Wave Rectifier (c) Bridge rectifier and trace it input and output by usingCRO. Also Study the L-type and π-type filter circuit.

Equipment Required: A step down transformer, P-N junction diodes, a high resistance, a

voltmeter, a ammeter, multimeter, a cathode ray oscilloscope, connecting wires.Learning Objectives:

Input current Iac and Input Voltage Vac

Output current Idc and output voltage Vdc

Voltage Regulation Factor with and without filter

Rectifier Efficiency with and without filter.

Varying the RL you can compare effect of load on circuit output.

You can trace the output using CRO to visualize the changing in output of

circuit with respective change in various electronic parameters of circuit.


1) Set the circuit as shown in circuit diagram for both half wave and full wave

rectifier.

2) Study the entire crux mentioned under learning objectives.

3) Do the required calculations and trace out the output.

4) Repeat all these steps for different value of load RL.

5) Full wave Rectifier with ∏-type filter: Close the switch S to bring both the

semi-conductor diodes D1 and D2 in circuit so that the arrangement acts as a full wave

rectifier. Also close switches S1 and S2 to get a ∏-type filter. Connect the terminals A1

and B1 to the y-y plate of C.R.O. Connect the primary of the transformer T to A.C.

mains supply and switch on the key K. Obtain the pattern of the full wave rectifiedvoltage through the ∏-type filter on the C.R.O. screen and trace it.

6) Full Wave Rectifier with L-type filter: Switch off S1 keeping S2 closed so

that L-type filter consisting of choke coil L and capacitor C2 is only in circuit. Repeat

all observations in step 2, 3 and 4.

Circuit Diagram:




Fig 1: Half Wave Rectifier

Fig2: Full – Wave rectifierFig 3: Bridge Rectifier




Fig 4: Full wave rectifier with L filter

Fig5: π filter

Observations:

Half Wave Rectifier

S. No Resistance Vac Vdcγ=

dc

ac

V

V

Full Wave Rectifier


dc

ac

V

V




Bridge Rectifier


dc

ac

V

V

Full Wave Rectifier with L filter


dc

ac

V

V

Full Wave Rectifier with pi filter


dc

ac

V

V

Plots and Parameters:

Trace of Output waveform of HWR and FWR with and without the useof filters.

Ripple Factor

Scope of Results:

You can trace the output of both HWR and FWR in this experiment and study the response of

circuit under different conditions.

Voltage regulation is the ability of a rectifier to provide near constant voltage over awide range of load conditions. It is a dimensionless quantity defined as:

Where V nl is voltage at no load and V fl is voltage at fullload. A smaller value of VR is usually beneficial.

Current Regulation of a circuit can also be studied by using the current as astudy parameter instead of voltage.

Rectification or Power Efficiency can be defined as ratio of output d.c

power available at load to input d.c power from the mains.

Rectification

where ,

http://en.wikipedia.org/wiki/Voltage

http://en.wikipedia.org/wiki/Electrical_load

http://en.wikipedia.org/wiki/Dimensionless_quantity

http://en.wikipedia.org/wiki/Dimensionless_quantity

http://en.wikipedia.org/wiki/Electrical_load

http://en.wikipedia.org/wiki/Voltage




The rectification of HWR and FWR ideally is 40.53% and 81.06% respectively.

Cautions:

A safely resistance must be connected in series with the load to avoidexcessive current.

To find the effective value of a.c. component a blocking capacitor of 16µf capacitance must be used.

The load in the output circuit must be varied by changing the resistance

by 1kΩ at a time.




Experiment No. 7: To determine the coefficient of self-inductance of unknown coil by

Anderson‟s method using a headphone.

Equipment Required: Inductance coil, Capacitor, Two variable resistances, Galvanometer,

headphone, audio oscillator



(a).Balancing point of the Wheatstone bridge.

(b). Self-inductance of the unknown coil

(c). Unknown capacity of capacitor can be determined.


According to circuit diagram using a battery in place of A.C. Source andgalvanometer in place of headphone make the connections.

Make Resistance P = Q

Taking a suitable value of R adjust the value of S so as to get a null point. Notethe values of resistances P and R.

Now replace the galvanometer by a headphone and battery by A.C. source youwill hear a sound in headphone.

Reduce the sound to minimum or zero value by varying the variable resistance rby keeping all other resistances constant out of which three are already constant.

This is the balance point for alternating current. Note the value of r for whichsound in minimum or zero.

Note the value of capacitance marked on it. Repeat it three times by changing thevalue of capacitance.





The self inductance of unknown coil is ------- L. This experiment can be used to

calculate the unknown capacity of capacitor.

Parameters and Plots:

Capacitance C =

Resistance P = Q = Ω

Resistance R = Ω

Resistance r = (i) Ω (ii) Ω (iii) Ω

Mean r = Ω

Inductance L= CR (P+2r)

Cautions:

Balancing point should be clearly noted.

Sound should be reduced to minimum value or zero before noting balancing point.




The resistance used should be non-inductive

Error analysis:-Probable error:-

Probable error = Standard Error

=

Where S =2

Δ = n – mean value of frequencym is the number of readings taken.

S.NO. Inductance of coil Δ Δ2

Percentage error:-

%age error = (actual value – measured value/ Actual value) * 100




Experiment No. 8: - To study Hall-effect by using hall probe. (Germanium crystal).

Equipment Requirement: -Hall probe, Gauss probe, Gauss meter, electromagnet,

constant current power supply, digital voltmeter.Material used: Ge crystal

Learning objectives: - When a magnetic field is applied perpendicular to a current

carrying conductor, a voltage is developed in a specimen in a direction perpendicular toboth the current and the magnetic field. This phenomenon is called the Hall Effect. The

voltage is so produced is called hall voltage. When the charges flow, a magnetic fielddirected perpendicular to the direction of flow produces a mutually perpendicular force

on the charges. Consequently the electrons and holes get separated by opposite forces andproduce an electric field. , there by setting up a potential difference between the ends of

specimen. This is called hall potential.

Outline of Procedure:-1. Place the specimen at the centre between the pole pieces and exactly perpendicular to

the magnetic field.

2. Place the hall probe at the centre between the pole pieces, parallel to the semiconductor

sample and note the magnetic flux density from the guess meter keeping the currentconstant through electromagnet.

3. Before taking the reading from the gauss meter ensure that gauss meter is showing zerovalue. For this put the probe away the electromagnet and switch on the gauss meter and

adjust zero.4. Do not change the current in the electromagnet for the first observation.

5. Vary the current in small increment. Note the current and the hall voltage.

6. For the 2nd

observation keep the current constant through the specimen and vary the

current through electromagnet and note the hall voltage.

7. Plot the graph between the hall voltage and the current through electromagnet .

Observations:




Current through the electromagnet = A(Constant)Magnetic field (as measured by the Gaussmeter) =

S.

No

Current through

Hall probe I (in )

Voltmeter readingHall

Voltage, V=

VH

‟

- VH

with magnetic

field,VH‟

without magnetic

field,VH

1

Current through the specimen = mA(Constant)

S.No

Current through

Electromagnet I‟

( in )

Voltmeter readingHall

Voltage, V=

VH‟ - VH

with magnetic

field,VH‟

without magnetic

field,VH

1

Scope of Result: - The graph between the VH and I, VH and I‟ is the straight line.

Parameters & Plots: -

The current density J = I / A

I = n E v A

The hall coefficient is given RH = VH b / IB,

where b = thickness of the specimen, VH = Hall Voltage, I = Current through the specimen,

B = Magnetic Field




The hall coefficient …………………m3 /

C

Caution:-

1. The hall probe should be placed at the centre of the electromagnet.

2. The specimen should be placed at the centre of the electromagnet.

3. Zero should be ensured in the gauss meter before placing the hall probe between the

centre of electromagnet.




Experiment No. 9: To study the characteristics of pnp and npn transistor (CE and CB).

Equipments Required: A pnp and npn transistor, Two voltmeters, Two milliammeters, a

potentiometer of total resistance of the order of one mega ohm, Batteries, connecting wires.



Set the transistor circuit to study its input/output characteristics with proper biasing.

Study the active, cut-off and saturation region.

Comparison of CB and CE characteristics

Circuit diagram: From C.L Arora (Ch 51)


Common base characteristics of the PNP transistor: Base is common to input and output

circuit. To draw the input characteristics, adjust the values of VCB (fix at one point) and

increase the VEB from zero onwards note IE.

To draw the output characteristics, adjust the values of IE at some fixed value and increase the

value of VCB from zero onwards and note IC.

Common emitter characteristics of the PNP transistor: Emitter is common to input and

output circuit. To draw the input characteristics, adjust the value of VCE (fix at one point) and

increase the value of VEB from zero onwards and note the value of IB.

To draw the output characteristics, adjust the values of IB at some fixed value and increase the

value of VCE from zero onwards and note IC.

Parameters & Plots:

IE=Emitter current, IB=Base current, IC=Collector current, VEB=Emitter to base voltage,

VCB=collector to base voltage, VCE = Collector to emitter voltage.

Characteristics of Transistor: There are two types of characteristics.

(A) Input:

For Common Base: Between IE and VEB at constant values of the collector voltages.

For Common Emitter: Between IB and VBE at constant values of the collector voltages.

(b) Output:




For Common Base: Between IC and VCB at constant value of emitter current.

For Common Emitter: Between IC and VCE at constant values of the collector voltages.

Plots of data:

Common Base configuration:

Input characteristics Output characteristics

Common Emitter Configuration:




Input characteristics Output characteristics

Cautions:

1. If the collector voltage exceeds the breakdown voltage for the junction the result may vary.2. If in a PNP transistor the emitter is not given the positive potential with respect to the base

and collector a negative voltage with respect to the base then the result may vary.

3. The leads of the transistor should be connected in the right way, the collector and theemitter junctions should not be interchanged.




Experiment No. 10: To compare the frequencies of oscillations produced by two audio-

oscillators using Lissajous figures.

Equipment Required: A standard 1000 Hz audio-oscillator, a variable frequency audio-

oscillator and cathode ray oscilloscope.



To draw the lissajous figure.

From the lissajous figure the Phase difference can be calculated.

Compare the frequencies of two audio oscillators.


1. Connect the standard frequency [1000 Hz] oscillator to the vertical input terminal of

the oscilloscope. Connect the audio oscillator whose frequencies are to be compared

with the standard oscillator to the horizontal frequency input terminal .Connect

together the ground terminals of both the oscillators.

2. Set the CRO so that the sharp, bright spot is obtained at the centre of the screen. Set

the audio oscillator frequency to the marked value of 1000Hz.

3. Switch on both the oscillators and adjust the gain control of the oscillators as well

as the horizontal and vertical gains of the oscilloscope so that a good size ellipse

appears on the screen. The actual frequency oscillator frequency is now

1000Hz.Record the dial reading.

4. Set the oscillator frequency to the marked value of 500 and adjust slowly so that a

1:2 Lissajous figure is obtained. Record the dial reading.

5. Similarly obtain (1:3,3:1), (2:3,3:2) Lissajous figure and so on up to (1:5,5:1).

Observations:

Vertical input standard frequency = 1000Hz

Hor. Input

Marked dial

Shape of fig No. of tangency points Vertical Freq.

Horizontal Fre

Actual Hor. Fr

On X-axis On Y-axis

Scope of the results expected: Actual Horizontal frequency

Parameters and Plots: NA

Cautions:




The vertical and horizontal gain controls of the oscilloscope should be adjusted toobtain a proper size of Lissajous Figure.

The sensitivity depends upon the amplifier gain. The gain control knob should notbe disturbed during the experiment.

The frequency of the audio-oscillator should be slowly adjusted so as to lock the

pattern.




Experiment 11 : To find the wavelength of He-Ne laser by using Michelson

interferometer.

Learning objectives:

To determine the wavelength of monochromatic light (He-Ne Laser).

To study the phenomena of interference of light.

Apparatus: A Michelson interferometer, He-Ne Laser, collimating lens, screen,

magnifying lens.

Diagram:

Fig. 1

Fig. 2

Outline of the procedure

First put the interferometer on a rigid table and level the instrument with three

leveling screws provided at the base.

Put the Helium-Neon laser, about 50 to 60 cm away from the instrument such that

its beam passes through the pin hole fitted in front of the instrument. Make sure

that the laser beam falls at the middle of the Mirrors M 1 and M2 after getting split

from beam splitter plate G1.




The beam after the reflections will make four spots on the wall or on a screen.

One pair is formed due to partial reflections at the unsilvered surface of G1 and

reflections at M1 and M2 respectively. While the other pair is formed due to

partial reflections at M1 and M2 respectively. Out of these one pair is brighter than

the other.

Now mirrors M1 and M2 are tilted carefully such that the two brighter images

coincide.

Now the instrument is aligned and the fringes are formed on the wall or screen.

The mirror M2 is kept fixed and the mirror M1 is moved with the help of the fine

movement screw and the number of fringes that cross the field of view is counted.


The student will be able to find the wavelength of He-Ne laser with the help of

interference phenomena and will come to know about the role of path difference in

interference of light.

Parameter and Plots:

Take any value of n≥20 and note down the value of distance (d) through which the mirror

is moved and apply theory of interference of light to find wavelength of light. [Report

data in tabular or systematic manner]

Caution:

Do not use the telescope.

Do not see directly into the laser beam.

Make sure that the distances of mirror M1 and M2 are almost equal from beam

splitter G1.

Make sure that centre of the circular fringes are properly adjusted.




Experiment 12: To study the output characteristics of FET/MOSFET

Objective:

a) To study Drain Characteristics of a FET.b) To study Transfer Characteristics of a FET

Equipment Required: JFET, Resistance, Power Supply, Ammeter, Voltmeter, Bread

Board and Connecting Wires.

Circuit Diagram:

DRAIN CHARACTERISTICSDetermine the drain characteristics of FET by keeping V GS= 0v.Plot itscharacteristics with respect to VDS versus ID TRANSFER CHARACTERISTICS

Determine the transfer characteristics of FET for constant value of VDS.Plot its characteristics with respect to V GS versus ID Graph (Instructions):1. Plot the drain characteristics by taking VDS on X-axis and ID on Y-axis atconstant VGS.

2. Plot the Transfer characteristics by taking VGS on X-axis and ID on Y-axisatconstant VDS




Calculations from Graph:

Drain Resistance (rd):It is given by the ration of small change in drain to source voltage (∆VDS) tothecorresponding change in Drain current (∆ID) for a constant gate to sourcevoltage(VGS),when the JFET is operating in pinch-off or saturation.egion.

Trans-Conductance (gm):Ratio of small change in drain current (∆ID) to the corresponding change ingateto source voltage (∆VGS) for a constant V DS.gm = ∆ID / ∆VGS at constant VDS .(from transfer characteristics) The value of gm isexpressed in mho’s or siemens (s).

Amplification Factor (µ):It is given by the ratio of small change in drain to sourcevoltage (∆VDS) to thecorresponding change in gate to sourcevoltage (∆VGS) for a constant draincurrent.µ = ∆VDS / ∆VGS.µ = (∆VDS / ∆ID) X (∆ID/∆VGS)µ = rd Xgm.

Inference:1. As the gate to source voltage (VGS) is increased above zero, pinch off voltageisincreased at a smaller value of drain current as compared to that when VGS =0V

2. The value of drain to source voltage (VDS) is decreased as compared to thatWhen VGS =0V

Result:1. Drain Resistance (rd) = …………. 2. Transconductance (gm) = …………. 3. Amplification factor (µ) = ………




Experiment 13: To draw the forward and reverse characteristics of P-N junctiondiode and draw load line. Objective:

1. To plot Volt-Ampere Characteristics of Silicon P-N Junction Diode.

2. To find cut-in Voltage for Silicon P-N Junctiondiode.3. To find static and dynamic resistances in both forward and reverse Biased

conditions for P-N Junction diode.

Equipment Required:

PN Junction Diode Resistance 1k ohm Regulated power supply(0 – 30V) 104 Ammeter mC (0-30)mA, (0-500)µA105 Voltmeter mC

(0 – 1)V, (0 – 30)V 106 Bread board and connecting wiresReverse BiasHere the anode of the diode is connected to the negative terminal of battery

andcathode of the diode is connected to positive terminal of the battery.

Circuit Diagram:

Forward Biased:

Reverse Biased:

For reverse biased , observer should reverse the polarity of battery.




Forward Biased Condition:

1. Connect the PN Junction diode in forward bias i.eAnode is connected topositive of the power supply and cathode is connected to negative of the power supply.

2. Use a Regulated power supply of range (0-30)V and a series resistance of 1kΏ.

3. For various values of forward voltage (V f ) note down the correspondingvaluesof forward current(If )

Reverse biased condition:1. Connect the PN Junction diode in Reverse bias i.e; anode is connected to negative of

the power supply and cathode is connected to positive of the power supply.2. For various values of reverse voltage (Vr ) note down the corresponding values

of reverse current ( Ir )

Tabular Column:

Forward Biased:

S.no (Vf ) (If )

1

2

Reversed Biased:

S.no (Vr) (Ir)

1

2

Graph ( instructions) :1. Take a graph sheet and divide it into 4 equal parts. Mark origin at the center of

thegraph sheet.2. Now mark +ve x-axis as( Vf ), -ve x-axis as (Vr ) ,+ve y-axis as (If ) , -ve y-axis as (Ir).

3. Mark the readings tabulated for diode forward biased condition in first QuadrantandDiode reverse biased condition in third Quadrant.

Calculations from Graph:

Static forward Resistance R dc= Vf /If Ω

Dynamic forward Resistance rac= ∆Vf /∆If Ω Static Reverse Resistance R dc=Vr /Ir Ω Dynamic Reverse Resistance rac= ∆Vr /∆Ir Ω

Load Line:




Result:Thus the VI characteristics of PN junction diode is

verified.1. Cut in voltage = ………V

2. Static forward resistance = ……….Ω

3. Dynamic forward resistance = ………. Ω Cautions:

1. While doing the experiment do not exceed the ratings of the diode. This maylead to damage of the diode.2. Connect voltmeter and Ammeter in correct polarities as shown in the circuitdiagram.3. Do not switch ON the power supply unless you have checked theCircuit connections as per the circuit diagram.

lmphy122

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