MBOSE Class 12 Question Paper 2024 for Physics

Meghalaya Board of School Education

QUESTION
PAPERS

Total No. of Printed Pages—11
HS/XII/Sc/Ph/24

2024

PHYSICS

( Theory )

Full Marks : 70

Time : 3 hours

The figures in the margin indicate full marks for the questions

General Instructions :

(i) There are 31 questions in all. All questions are
compulsory.

(ii) This Question Paper has four Sections : Section—A
(Part—I and Part—II), Section—B, Section—C and
Section—D.

(iii) Section—A (Part—I) contains five multiple choice
questions of 1 mark each and Section—A (Part—II)
contains five questions of 1 mark each. Section—B
contains nine questions of 2 marks each, Section—C
contains nine questions of 3 marks each and
Section—D contains three questions of 5 marks each.

(iv) There is no overall choice. However, internal choices have
been provided in three questions of 1 mark, four
questions of 2 marks, five questions of 3 marks and all
the three questions of 5 marks weightage. You have to
attempt only one of the choices in such questions.

/29 [ P.T.O.

( 2 )

(v) You may use the following values of physical constants,
wherever necessary :
c = 3 ´ 10 8 m/s

h = 6 × 63 ´ 10 -34 J-s

e = 1 × 6 ´ 10 -19 C

m 0 = 4p ´ 10 -7 T m A -1

e 0 = 8 × 854 ´ 10 -12 C2 N -1 m -2

m e = 9 × 1 ´ 10 -31 kg

Mass of neutron = 1·00867 amu = 1 × 675 ´ 10 -27 kg
Mass of proton = 1·00728 amu = 1 × 673 ´ 10 -27 kg
Mass of a-particle = 4·00152 amu = 6 × 646 ´ 10 -27 kg

SECTION—A
PART—I
( Multiple choice type questions )

Choose and write the correct option for the following : 1×5=5

1. The core in transformers and other electromagnetic
devices is laminated, so as to

(a) increase the magnetic field

(b) increase the magnetic flux

(c) reduce the magnetism in the core

(d) reduce the eddy current losses in the core 1

HS/XII/Sc/Ph/24/29 [ Contd.

( 3 )

2. In Young’s double-slit experiment, a monochromatic ray
of light of wavelength 5 ´ 10 -5 cm falls on double-slit of
slit width 0·025 mm. If the phenomenon of interference is
observed on the screen at a distance of 5 cm, the fringe
width becomes
(a) 0·1 mm
(b) 1 mm
(c) 0·01 mm
(d) None of the above 1

3. A short bar magnet placed with its axis at 30º with an
external magnetic field of 800 G experiences a torque of
0·016 N-m. What is the magnetic moment of the magnet?
(a) 0·40 A-m2

(b) 0·004 A-m2

(c) 0·80 A-m2
(d) 0·02 A-m2 1

r r
4. If E and B represent electric and magnetic field vectors of
the electromagnetic waves, then the direction of
propagation of the electromagnetic waves is that of
r
(a) E
r
(b) B
r r
(c) E ´ B
r r
(d) E × B 1

HS/XII/Sc/Ph/24/29 [ P.T.O.

( 4 )

5. n-type semiconductor is obtained by doping the intrinsic
semiconductor with
(a) trivalent material
(b) conductor
(c) insulator
(d) pentavalent material 1

PART—II
( Very short answer type questions )

Answer each of the following questions in 1 sentence/step : 1×5=5

6. Either

If an intrinsic semiconductor is doped with a monovalent
material, what type of extrinsic semiconductor will we
get? 1
Or
What happens to the width of the depletion layer when
the junction is under reverse bias? 1

7. What is meant by the term doping? 1

8. Either

Why is there no photoelectric current at frequencies below
threshold frequency? 1
Or
Write down the Einstein photoelectric equation. 1

HS/XII/Sc/Ph/24/29 [ Contd.

( 5 )

9. Either

A semi-circular arc of radius 20 cm carries a current of
10 A. What is the magnitude of the magnetic field at the
centre of the arc? 1
Or
A galvanometer with a coil of resistance 12 × 0 W shows
full-scale deflection for a current 2·5 mA. How will you
convert the galvanometer into an ammeter of range 0 to
7·5 A? 1

10. Arrange the following electromagnetic radiations in
descending order of their frequencies : 1
X-rays, Visible light, Ultraviolet rays, Radio waves

SECTION—B
( Short answer type–I questions )

Answer each of the following questions within 20 to 30 words,
wherever applicable : 2×9=18

11. Either

What is nuclear fusion? Write the underlying principle of
atom bomb. 1+1=2
Or
Write two defects of Rutherford’s atomic model. 2

12. Either

The radii of curvature of a double-convex lens are 15 cm
and 30 cm and its refractive index is 1·5. Calculate its
power. 2

HS/XII/Sc/Ph/24/29 [ P.T.O.

( 6 )

Or
A convex lens of focal length 30 cm and a concave lens of
focal length 60 cm are placed in contact. Find the power
of the combination. 2

13. An iron-cored solenoid and a bulb are connected to an
a.c. source. If the iron core is removed from the solenoid,
the brightness of the bulb decreases. Why? 2

14. Either

State two conditions to be fulfilled by a ray of light in the
phenomenon of total internal reflection. Name one
2
technological application of total internal reflection.
Or
State two conditions, which must be satisfied for two light
sources to be coherent. Can two independent sources of
light be coherent? 2

15. Show that the de Broglie wavelength of an electron
h
of kinetic energy K is given by l = , where m is the
2mK
mass of electron and h is Planck’s constant. 2

16. Either

The ground state energy of H-atom is 13·6 eV. What are
the kinetic and potential energies of the electron in this
state? 2
Or
A hydrogen atom initially in the ground level absorbs a
photon which excites it to the n = 4 level. Determine the
wavelength and frequency of the photon. 2

HS/XII/Sc/Ph/24/29 [ Contd.

( 7 )

17. An n-type semiconductor has a large number of electrons
but still it is electrically neutral. Explain the reason. 2

18. A student performs an experiment on photoelectric effect
using two materials A and B. A plot of stopping potential
(V 0 ) and frequency (n) is given in the figure :

6
B
5
V0 A
4
(volt)
3
2
1
0
5 10 15 20
n (1014 Hz)

Which material, A or B, has greater work function (f)?
Justify your answer. 2

19. Write Biot-Savart law in vector form. What is the
limitation of Biot-Savart law? 1+1=2

SECTION—C
( Short answer type–II questions )

Answer each of the following questions within 30 to 40 words,
wherever applicable : 3×9=27

20. Either

Draw a ray diagram of an astronomical telescope showing
the final image at infinity and write the expression of its
magnifying power. 3

HS/XII/Sc/Ph/24/29 [ P.T.O.

( 8 )

Or
With the help of a ray diagram, show that the total
deviation of a ray of light passing through a glass prism is
given by d = i + e - A, where the symbols used carry usual
meanings. 3

21. Either

Distinguish between conductors, semi-conductors and
insulators on the basis of band theory of solids. 1+1+1=3
Or
Draw a circuit diagram of a full-wave rectifier. Explain its
working and show the input, output waveforms. 1+1+1=3

22. State Ampere’s circuital law. Using this law, obtain the
expression for the magnetic field near an infinitely long
current-carrying wire. 1+2=3

23. Either

Write the expression of Lorentz force. Obtain the force on
a current-carrying conductor in a uniform magnetic field.
1+2=3
Or
What is a magnetic moment? Obtain the magnetic
moment of a revolving electron around the nucleus. 1+2=3

24. Give one point of difference between the e.m.f. and the
terminal potential difference of a cell. Show that the
E -V ö
internal resistance of a cell is r = æç ÷ × R , where E
è V ø
and V are the e.m.f. and potential difference of the cell
and R is the load resistance. 1+2=3

HS/XII/Sc/Ph/24/29 [ Contd.

( 9 )

25. Either

Show that the torque acting
r onran electric dipole placed in
r r r r
a uniform electric field E is t = p ´ E , where p and t
represent the dipole moment and torque respectively. 3
Or
What is resistance of a resistor? Show that the equivalent
resistance of three resistors connected in series is equal to
the sum of the resistances of the individual resistors.
1+2=3

26. Using Kirchhoff’s laws in the electrical network, calculate
I 1, I 2 and the rate of dissipation of energy in R2 : 1+1+1=3

E1 = 12 V R1 = 2 W

I1

R2 = 4 W

I1 + I2

I2

E2 = 6 V R3 = 1 W

27. Either

The relative magnetic permeability of a magnetic material
is 800. Identify the type of the magnetic material and state
two of its properties. 1+2=3
Or
What are magnetic field lines? Can two magnetic field
lines intersect? Justify your answer. 1+1+1=3

HS/XII/Sc/Ph/24/29 [ P.T.O.

( 10 )

28. What holds nucleons together in the nucleus? Calculate
the binding energy of an a-particle. 1+2=3

SECTION—D
( Long answer type questions )

Answer each of the following questions within 70 to 80 words,
wherever applicable : 5×3=15

29. Either

What is electric flux? Using Gauss’ law, find the electric
field due to a uniformly charged thin spherical shell of
uniform surface charge density (s ) at a point (a) inside the
shell and (b) outside the shell. 1+2+2=5
Or
What are polar and non-polar molecules? Deduce an
expression for the capacitance of a capacitor with a
dielectric substance of dielectric constant K and
thickness t such that the thickness is less than the
separation between the plates (d ). 1+1+3=5

30. Either

Give the construction and theory of an a.c. generator.
2+3=5
Or
Derive an expression for average power in L-C-R circuit
connected to an a.c. supply. What is wattless current?
4+1=5

HS/XII/Sc/Ph/24/29 [ Contd.

( 11 )

31. Either

What is a wavefront? Establish the laws of refraction on
the basis of Huygen’s principle. 1+4=5
Or
What is interference of light waves? Deduce analytically
the conditions for constructive and destructive inter-
ference of two coherent light waves. 1+2+2=5

HHH

HS/XII/Sc/Ph/24/29 24K—5410

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