LMPHY122

Approved for Autumn Term Session 2010-11 1

PHYSICS LAB MANUAL

Course Code: PHY122 Course 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


TEXTBOOK:

1. LMPHY122.doc

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

2007

S. No Title of Experiment Page No.

1 An introduction to units, errors ,different types of graphs and measurement of length, mass and time. 3-8

2 To study the variation of magnetic field with the distance along the axis of circular coil carrying current by plotting a graph.

9-10

3 To compare the frequency of oscillation produced by the two audio oscillator using Lissajous figures.

11

4 To plot a graph between current and frequency in LCR series and parallel circuit and find resonant frequency, quality factor and band width.

12-14

5

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 using CRO. Also Study the L-type and π-type filter circuit.

15-18

6 To study the induced e.m.f. as the function of velocity of the magnet 19-20

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

21-22

8 To determine Hall Voltage and Hall Coefficient using Hall Effect. 23-24

9 To study the characteristics of PNP and NPN transistor (CE and CB). 25-27

10 To determine the frequency of an electrically maintained tuning fork using CRO. 28-29


Experiment 1 Title :- An introduction to units, errors ,different types of graphs and measurement of length, mass and time. Equipments to be used :- Vernier calliper, travelling microscope, and screw gauge etc.

Material Required:- Simple graphs papers

Learning objective:-

1.To find the least count of various measuring instrument.

2.How to plot graphs?

3.Error Analysis

Units. The measurement of the physical quantities should be done in the most convenient unit e.g. mass of the

body in grams, measurement using vernier calliper in cm, small current in mA etc. All the measured

quantity must be converted into SI unit while tabulating.

Least count.

Least Count= (Value of one main scale division) / (Total no. divisions on the vernier scale)

Observed Reading=M.S. reading+ V.S. reading

Note: find out the the least count of the measuring instrument available in the lab

e.g vernier calliper, screw gauge, spectrometer, Michelson Interferometer, etc.

A graph is a straight or curved which shows the relative change between two quantities out of which

one varies as a result of change in the other. The quantities which is changed at will is called

independent variable while alter due to the change in the first is called dependent variable. The point

where the axes of independent and dependent variable meet at right angle is called origin.

Following rule must be adopted while plotting a graph

1. Find the independent and dependent variables. Plot the independent variable along X-axis and

the dependent variable along the Y-axis. 2. Determine the range of each variable and count the no of divisions available on the graph to

represent the each variable along the respective axes.


3. Choose a convenient scale for both variables .It is not necessary to have the same scale for

both.The scale should neither be too narrow nor too wide.It is preferable that 10 divisions

should be represent 1,2,5, or 10 or their multiples by any +ve or –ve power of 10. We must see

that maximum portion of the graph paper is utilized and the graph is well within it.

4. At least six observation extending over a wide range should be taken for plotting the graph.

5. If the relation between the two variables begins from zero of if zero value of one of one of the

variables is to be found out, it is necessary to take origin as zero along both the axes.

6. The origin need not always be represent by zero. Its value should be round number less than

the smallest given value of the independent or dependent variable.

7. It is not necessary to write all the values along the respective axes.

8. Mark the point with a pencil. Draw a small circle or put a cross to indicate the plotting point

prominently.

9. Draw a smooth free hand curve through the plotted points. It is not necessary that the curve

should pass through every point leave as many points below it as there are above it.

10. The title graph should be given boldly near the top of the graph paper.

11. It is always better to indicate the scale for both the variable at the top in the left or right corner

of the graph paper.

Linear graphs Example 1 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 be re-written as

T2 = (4gL---------(2)

Eq. (2) is an equation of straight line with slope = (4gand intercept = 0 A student came up with the following data.

S.No T (s)

L (cm)

1 1.0 24.8 2 0.9 20.1 3 0.8 15.9 4 0.7 12.2 5 0.6 8.9 6 0.5 6.2

Find the value of “g” by graphical analysis.


How to draw the graph? Step 1. From Eq. 2 we have to plot T2 vs L so our table is (L should in meters)

S.No T2 (s)

L x 10-2 (m)

1 1.0 24.8 2 0.81 20.1 3 0.64 15.9 4 0.49 12.2 5 0.36 8.9 6 0.25 6.2

Step 2. Choose a “linear” graph sheet which is linearly (normally in mm) graduated on both X- as well Y- axis. Step 3. Choose Y-axis for T2 and X-axis for L Step 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 pencil Step 6. Draw a straight line through the points so that maximum number of points are on/very close to the line (Best fit we will not discuss presently) Step 7. Find the slope from the graph and calculate “g” 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

gh (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 table

S.No gh m/s2

h m

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 4.0 670.0 5.0 600.0 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 graph Planetary period ‘T’ (in earth years) is related to its distance ‘R’( AU, astronomical units; 1AU is equal to average separation between earth and sun) by the relationship of the form

T = kRn Calculate ‘k’ and ‘n’ by graphical analysis from the following data

T = kRn or log T = log k + n log R

Plot 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.

Name of the planet T in Earth years

R in Astronomical 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


Error analysis Measurement is basic to science. A measurement is meaningful only if the uncertainties involved are specified. An operator “X” has to specify the uncertainty (error) in his final result; the practice of comparing the result with “standard value” is unscientific 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 comparing it 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 zero error, faulty calibration, error due to parallax, bias of the operator etc) and uncontrollable changes in experimental parameters like temperature, pressure, voltage etc. The instrument errors (systematic errors) are instrument specific, can be either +ve or –ve and are constant in nature. On the other hand errors due to changes in experimental parameters 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 or vernier 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)21/2 It shows how much deviation there is from the "average" (mean). A low standard deviation 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 measurement in 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 = Y2(X)2 +X2 ( 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 in Z 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/Y2 Z =(1/Y) 2(X)2 +[(X)2]/Y4 ( 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] ± [estimated error] 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 significant digits. If the object whose length was measured has breadth say 5.41±0.05cm (measured with 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)21/2 = 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 while error 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 experiments 1. 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 each instrument 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 count is 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 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

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 little above 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 vertical plane. 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 both ends. 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 direction and keeping the current constant at the same value. Observations. Least count of the magnetometer = Current I =


S. No Left Side Right Side

Distance from the centre,x (in )

Direct Reversed

Mean θ tan θ

Direct Reversed

Mean θ tan θ

Scope of the result to be reported Plots & 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 maximum at 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. The distance 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.


Experiment No. 3: 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. Material Required: NA Learning Objectives:

To draw the lissajous figure.

From the lissajous figure the Phase difference can be calculated.

Compare the frequencies of two audio oscillators.

Outline of the Procedure: 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

No. of tangency points Hor. Input Marked dial

Shape of fig

On X-axis On Y-axis

Vertical Freq. Horizontal Freq.

Actual Hor. Freq.

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 to obtain a proper size of Lissajous Figure.

The sensitivity depends upon the amplifier gain. The gain control knob should not be disturbed during the experiment.


The frequency of the audio-oscillator should be slowly adjusted so as to lock the pattern. Experiment No. 4- 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 is called 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 the value 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 Factor Maximum 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

Lr2

Calculated value of Q from inductance L = RC r )/1(

= rCR2

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 = CR

L1

=

(ii) R2 = CR

L2

=

Impedance at resonance Z =


Calculated value of current at (anti) resonance for

(i) R1 = Ev /Z = L

CREv 1

(ii) R2 = Ev /Z = L

CREv 2

Anti Resonant frequency, νr (graphically) =

Calculated value for R1 = 21

2

211

LR

LC

Calculated value for R2 = 21

2

221

LR

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. 4: 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 using CRO. 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. Outline of Procedure:

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 rectified voltage 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:

Half – Wave Rectifier


Fig 1: Half Wave Rectifier

Fig2: Full – Wave rectifier Fig 3: Bridge Rectifier

Fig 4: Full wave rectifier with L filter


Fig5: π filter

Observations:

Half Wave Rectifier S. No Resistance Vac Vdc γ=

dc

ac

VV

Full Wave Rectifier

S. No Resistance Vac Vdc γ= dc

ac

VV

Bridge Rectifier


ac

VV

Full Wave Rectifier with L filter


ac

VV

Full Wave Rectifier with pi filter


ac

VV

Plots and Parameters:

Trace of Output waveform of HWR and FWR with and without the use of 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 a wide range of load conditions. It is a dimensionless quantity defined as:

Where Vnl is voltage at no load and Vfl is voltage at full load. A smaller value of VR is usually beneficial.

Current Regulation of a circuit can also be studied by using the current as a study 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 ,

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 avoid excessive 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. 5: 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 stopwatch

Learning 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 = R0 0

Time for 20

Oscillations

Mean time

period(T)

eo eo/a= eo/ R0 0 Linear velocity

v = (2Π/T) R0 0

1

(i)

(ii)


.

.

.

(iii)

Mean

2

(B) Amplitude constant, time period variable: Sr.No. Amplitude

a = R0 0

Time for 20

Oscillations

Mean time

period(T)

eo eoT Linear velocity

v = (2Π/T) R0 0

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. 6: 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.

Outline of the Procedure: According to circuit diagram using a battery in place of A.C. Source and galvanometer 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. Note the values of

resistances P and R. Now replace the galvanometer by a headphone and battery by A.C. source you will hear a sound in

headphone. Reduce the sound to minimum or zero value by varying the variable resistance r by 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 which sound in minimum or zero.

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


Scope of the results expected:

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 frequency m 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. 7: - 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 to both 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 field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. Consequently the electrons and holes get separated by opposite forces and produce 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 current constant through electromagnet. 3. Before taking the reading from the gauss meter ensure that gauss meter is showing zero value. 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) =

Voltmeter reading

S. No

Current through Hall probe I (in )

with magnetic

field,VH’

without magnetic

field,VH

Hall Voltage, V=

VH’ - VH

1


Current through the specimen = mA(Constant)

Voltmeter reading

S. No

Current through Electromagnet I’

( in )

with magnetic

field,VH’

without magnetic

field,VH

Hall Voltage, V=

VH’ - 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. 8: 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)

Outline of Procedure:

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 the emitter junctions should not be interchanged.


Experiment No. 9: - To determine the frequency of an electrically maintained tuning fork using CRO. Equipment Requirement: - Electrically maintained tuning fork, battery, connecting wires, CRO, Audio frequency oscillator, rheostat, resistance box.

Learning objectives:-

o To draw the Lissajous figure Circuit Diagram

:

Outline of procedure:- (a) With CRO

Make the connection according to the circuit diagram. Switch on the power supply to the CRO and obtain a bright, sharp and fine spot of light at the

centre of the CRO screen by adjusting the intensity, focussing and positioning controls of the CRO.

Set the tuning fork into vibration by inserting the key K. As the tuning fork is vibrating an A.C. voltage is develop across the resistance R, which will trace a vertical line on the screen .Keep this line within the scale by adjusting the Y-amplifier gain.

Switch on the audio frequency oscillator and adjust its frequency so as to obtain the trace of a circle on the C.R.O screen. Trace the circle. The frequency produced by the audio oscillator for this trace is the same as the frequency of the tuning fork.

Now adjust the frequency of audio oscillator such that a figure of eight (8) appears in the vertical direction on the screen. Trace the figure and note the frequency produced by the audio oscillator. The frequency of the tuning fork will be one half the frequency produced by the audio oscillator.

Again adjust the frequency of the audio oscillator such that the figure of eight (∞) in the horizontal direction appears on the screen. Trace the figure and note the frequency produced by the audio oscillator. The frequency of the tuning fork will be double the frequency produced


by the audio-oscillator. Observations

Hor. Input

Frequency from the audio oscillator

Shape of fig

No. of tangency

points

Vert.freq./Hor.freq. Freq. of

tuning fork.

o

8

8

Parameters & Plots: Trace of patterns obtained on the C.R.O

Mean frequency=….. Hz

CAUTIONS:

While finding the vertical sensitivity both the horizontal deflecting plates must be earthed and vice versa.

The sensitivity depends upon the amplifier gain. The gain control knob should not be disturbed during the experiment.

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

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