CBCS Examination (C.U.) 2021 Sem 2 Physics (Honours) Paper : CC-3 (Practical)

Full Marks 30

Answer Script should be sent to the Email Id: physem1hajcbc@gmail.com

Answer any one question

1) a. Write the theory for the experiment ‘Determination of an unknown Low Resistance using Carey

Foster’s Bridge’. 8

b. Draw the circuit diagram and write the working formulae for determination of resistance per unit

length of the wire of the bridge and the unknown low resistance.

5+4=9

c. Following data are given. Calculate the resistance per unit length of the wire of the bridge.

Resistance (Ω) Position of balance point with copper strip in left gap, l (cm)

Position of balance point with copper strip in right gap, l′ (cm)

0.3 62.5 48.1

0.4 60.4 39.9

0.5 56.8 31.4

0.6 58.2 30.6

5

d. Calculate the resistance of an unknown low resistance from the data given below.

Resistance (Ω) l (cm) l′ (cm)

0.1 84.6 39.8

0.2 82.2 41.9

0.4 80.5 51.1

0.6 77.3 56.9

0.8 78.7 68.2

5

e. Why does the null point should be measured for both direct and reverse current? If we use mirror

galvanometer then what modification will you make to the circuit to save the galvanometer from

damage? What is the minimum difference in resistance that can be measured with this bridge wire?

1+1+1=3

2) a. Write down the theory and circuit diagram to measure the current flowing in a circuit with the help

of a potentiometer when a milliammeter is given for calibration.

b. Suppose, total length of the wire in given potentiometer is L=1000cm. Resistance, R= 20 Ohm.

Calculate the current, i, flowing in the circuit if the fixed resistance is r=1 Ohm. Table for null point is

given below:

Sl.

no.

Milliammeter

reading (I) in mA

Wire

number

Scale reading Total length

in cm (l)

p.d. across r is

e=IRl/(1000L) V

Mean e Current

i=e/r in A

1. 10 10th 96 960

2. 10.5 9th 80 880

c. Write the precautions that must be taken while performing the experiment.

[(10+6)+10+4]

3) a. Write down the theory and draw the circuit diagram for converting a given ammeter of range (0-

100 µA) into a voltmeter of range (0-2V).

b. From the given set of half deflection method data, obtain internal resistance of the ammeter:

Sl. No. Shunt resistance (Ω) Series resistance (Ω) Reading in ammeter (µA)

1 5 0 980

d= 100 d= 50

2 5 0 940

d= 90 d= 45

3 5 0 1030

d= 80 d= 40

4 5 0 990

d= 92 d= 46

5 5 0 1020

d= 88 d= 44

c) Find out the value of the series resistance to be connected in series to convert it into a voltmeter of

range (0-2V).

d) Write down the precautions that must be taken while performing the experiment.

e) What is the internal resistance of an ideal ammeter and voltmeter?

(8+6) +6+5+3+2

2021

PHYSICS — Honours

Paper- CC-4

Full Marks: 30

The figures in the margin indicate full marks.

Candidates are required to give their answers in their own words

as far as practicable.

Answer any one question :

1. (a) Draw a neat labeled diagram for performing the Newton’s ring experiment with a

plane glass slab and a plano-convex lens. (8)

(b) Write down the working formula to determine the wavelength λ using the Newton’s

ring apparatus. Indicate what the symbols represent. (5)

( c) Given below is the data for the diameters of the dark rings and their order numbers

as the microscope is moved from left to right and then again from right to left. Complete

the table and find out the mean value of the diameter for the dark ring of each

order (n). (5)

(d) Hence plot a [d2 vs n] graph and from this graph, find out the value of the

wavelength of the incident monochromatic light using the working formula, when the

radius of curvature of the curved surface of the plano-convex lens is 100 cm.

Take Vernier constant of the apparatus to be 0.01mm (5+2)

Ring no. P+n

Observation from

Reading of microscope for Diameter R1-R2 (mm)

Mean diameter Dn

(mm)

Left edge of ring right edge of ring

Main scale(mm)

Vernier scale

R1 Main scale(mm)

Vernier scale

R2

P+25 Left to right 44 98 37 83

Right to left 44 97 37 82

P+23 Left to right 44 83 38 07

Right to left 44 82 38 08

P+21 Left to right 44 64 38 24

Right left 44 66 38 26

P+19 Left to right 44 45 38 37

Right to left 44 45 38 33

P+17 Left to right 44 33 38 71

Right to left 44 32 38 69

P+15 Left to right 44 16 38 91

Right to left 44 15 38 89

P+13 Left to right 43 98 39 06

Right to left 43 97 39 05

P+11 Left to right 43 76 39 28

Right to left 43 75 39 27

P+9 Left to right 43 55 39 54

Right to left 43 54 39 53

P+7 Left to right 43 30 39 74

Right to left 43 29 39 73

P+5 Left to right 43 02 40 05

Right to left 42 99 40 01

(c) What kind of interference takes place in the Newton’s ring experiment? Where do

you think the fringes are formed? What are such fringes called? (2+2+1)

[8+5+5+(5+2)+5=30]

2. (a) Draw a neat ray diagram for obtaining interference fringes using the Fresnel’s

biprism and write down the working formula for determining the wavelength of a

monochromatic light using this set up (without index error). [8+2]

(b) Given the value of least count (l.c) of the circular scale (c.s) to be 0.01mm, find the

value of “d” by completing the following table using the formula 21ddd . [5]

(l.s linear scale; c.s circular scale)

Position of lens

Movement of eye piece

from

Reading of micrometer screw Dist. Between

the images m1~m2 (mm)

21ddd

(mm) Left image(a) Right image(b)

l.s (mm)

c.s Tot (mm)

Mean m1

(mm)

l.s (mm)

c.s Tot mm

Mean m2

(mm)

I Leftright 10 0 14 0 d1

Right Left 10 10 14 0

II Leftright 7.5 0 8 10 d2

Right Left 7.5 0 8 10

(c ) From the data given in the following table, determine the fringe width of the

interference fringes for two positions of the eye piece by completing the table. Hence

calculate the wavelength of the incident monochromatic light using the working

formula. [10]

Position of eyepiece

Movement of

micrometer

Reading of micrometer screw Dist between n bands

Mean R (mm)

Fringe width

n

R

(mm)

l.s (mm)

c.s Tot (mm)

Mean

(mm) Fringes taken from

Width of n fringes R (mm)

84cm Leftright 6.5 30 14 1.505 1

Right Left 6.5 32

Leftright 7.5 44 36 1.46

Right Left 7.5 40

Leftright 8.5 44 58 1.45

Right Left 8.5 37

Leftright 9.5 30 710 1.465

Right Left 9.5 28

Leftright 10.5 34 912 1.56

Right Left 10.5 30

92cm Leftright 8.0 45 14 1.615 2

Right Left 8.0 44

Leftright 9.5 10 36 1.55

Right Left 9 48

Leftright 10.5 16 58 1.576

Right Left 10.5 5

Leftright 11.5 20 710 1.505

Right Left 11.5 15

Leftright 12.5 25 811 1.525

Right Left 12.5 20

(d) What kind of interference takes place in Fresnel’s biprism? What do you mean by

virtually coherent sources? [2+3]

[(8+2)+5+10+(2+3)=30]