MBOSE Class 12 Question Paper 2025 for Physics

Meghalaya Board of School Education

QUESTION
PAPERS

Total No. of Printed Pages—11
HS/XII/Sc/Ph/25

2025

PHYSICS

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 type
questions of 1 mark each and Section—A (Part—II)
contains five very short answer type 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.

/229 [ P.T.O.

( 2 )

(v) You may use the following values of physical constants :
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 × 675 ´ 10 -27 kg
Mass of proton = 1 × 673 ´ 10 -27 kg
Avogadro’s number = 6 × 023 ´ 1023 per gram mole
Boltzmann constant = 1 × 38 ´ 10 - 23 J K -1

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

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

1. The capacitance of a parallel-plate capacitor with air
in between the plates is C. If an oil of dielectric
constant k = 2 is put between the plates, then the
capacitance will become
(a) C
(b) 2C
(c) C/2
(d) C/4 1

HS/XII/Sc/Ph/25/229 [ Contd.

( 3 )

2. R

I=0·5 A

In the circuit shown above, each cell has an e.m.f. of 2 V
and an internal resistance of 1 W. The current flowing
through the circuit is 0·5 A. The resistance of the
resistor R is
(a) 6 W
(b) 4 W
(c) 8 W
(d) 2 W 1

3. The magnetic field at the centre of a circular coil of
radius 5 cm carrying a current of 1 A is 1·256 T. If the
radius is made 10 cm, then the magnetic field at the
centre of the loop carrying same current will be
(a) 2·512 T
(b) 0·628 T
(c) 5·024 T
(d) 0·314 T 1

4. Monochromatic light of wavelength 4500 Å is incident
on a clean metal surface of work function 2·3 eV. The
maximum kinetic energy of the ejected photoelectrons
is 0·5 eV. Then the energy of the incident photon is
(a) 1·8 eV
(b) 2·8 eV
(c) 11·5 eV
(d) 12·5 eV 1

HS/XII/Sc/Ph/25/229 [ P.T.O.

( 4 )

5. A nucleus Z X A has mass represented by M (A, Z ). If M p
and M n denote the mass of proton and neutron
respectively and B × E , the binding energy in MeV, then
(a) B × E = M (A , Z ) - ZM p - (A - Z ) M n

(b) B × E = [ZM p + AM n - M (A , Z )]C 2

(c) B × E = [Z × M p + (A - Z ) M n - M (A , Z )]C 2

(d) B × E = [ M (A , Z ) - ZM p - (A - Z ) M n ]C 2
1

PART—II
( Very short answer type questions )

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

6. Either

The specific resistances of copper, silver and constantan
are 1 × 78 ´ 10 - 6 W-cm, 1 ´ 10 - 6 W-cm and 4 × 8 ´ 10 - 6 W-cm
respectively, which is the best conductor and why? 1
Or
In which way, the cells should be combined to get
maximum current, when the external resistance is very
high compared to the total internal resistance of the cells? 1

7. Either

The equation of an alternating current is I = 50 sin100t.
Find the frequency. 1
Or
A 100 hertz alternating current is flowing in a 14 mH coil.
Find its reactance. 1

HS/XII/Sc/Ph/25/229 [ Contd.

( 5 )

8. What is the de Broglie wavelength associated with an
electron, when accelerated through a potential difference
of 100 volt? 1

9. Either

You are given two convex lenses of focal lengths 10 cm
and 60 cm. To make a telescope, which of the two lenses
will you use as object lens and which one as an eye lens? 1
Or
A convex lens is immersed in water. How is power of the
lens affected? 1

10. The energy of the electron of H-atom is ground state is
–13·6 eV. What will be the energy of the electron in n = 3
orbit? 1

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

A parallel-plate capacitor is made of two foils, each of
surface area 2 m2 , separated by paper 7 ´ 10 -5 m thick.
What is its capacitance? (Take k = 3 × 5 for paper) 2
Or
An electric dipole consists of two opposite charges of
magnitude 1 mC each, separated by a distance of 3 cm.
The dipole is placed in a uniform electric field of
4 ´ 10 5 N/C. Find the maximum torque on the dipole. 2

HS/XII/Sc/Ph/25/229 [ P.T.O.

( 6 )

12. Write down the condition of resonance in series L-C-R
circuit and hence find an expression for the resonant
frequency. ½+1½=2

13. Either

An L-C-R series circuit is connected to an AC source as
shown in the figure below :
R =400 W L = 0·4 H C = 10–5 F

EV =100 V

If w = 1000 radian/sec, then find the impedance of the
circuit. 2
Or
Find the root mean square value of current through a
capacitor of capacitance 10 mF, when connected to an
AC source of 110 volts at 50 cycles/sec supply. What is its
reactance? 2

14. Which waves are used in radar system? Give their
frequency range and mention the source of their
production. 2

15. Find the wavelength of electromagnetic waves of
frequency 5 ´ 1019 Hz in free space. Identify the type of
electromagnetic waves. Give one application of it. 1+½+½=2

HS/XII/Sc/Ph/25/229 [ Contd.

( 7 )

16. Either

Write down the conditions for constructive and
destructive interference in terms of path difference of two
coherent light waves. 1+1=2
Or
What is critical angle? Derive the relation between the
critical angle and the refractive index of the denser
medium relative to the rarer medium. 1+1=2

17. Either

According to Rutherford’s model of atom, what is ‘impact
parameter’? Write down the relation between the impact
parameter and scattering angle. 1+1=2
Or
In hydrogen atom, an electron undergoes transition from
third excited state to the second excited state and then
to the first excited state. Identify the spectral series to
which these transitions belong. Find out the ratio of the
wavelength of the emitted radiations in the two cases.
1+1=2

18. What are extrinsic semiconductors? Name the types of
extrinsic semiconductor obtained when germanium is
doped with (a) arsenic and (b) gallium. 1+½+½=2

19. Define the term ‘potential barrier’. How does the thickness
of depletion region change when p-n junction is reverse
biased? 1+1=2

HS/XII/Sc/Ph/25/229 [ P.T.O.

( 8 )

SECTION—C
( Short answer type–II questions )

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

20. Using Gauss’ theorem, derive an expression for electric
field intensity at a point due to an infinite plane sheet
of charge. 3

21. Either

Deduce a relation between the drift velocity and current
flowing through a conductor. Using the magnitude of drift
velocity in the relation, show that
ml
R=
nAe 2 t
where the symbols have their usual meanings. 1+2=3
Or
Apply Kirchhoff’s laws to obtain the condition of balance
of a Wheatstone bridge. 3

22. Either

Obtain an expression for the torque acting on a
rectangular current loop, when placed inclined at an
angle q with the direction of a magnetic field. 3
Or
Using Ampere’s circuital law, find an expression for the
magnetic field at a point well inside straight solenoid
carrying current. 3

HS/XII/Sc/Ph/25/229 [ Contd.

( 9 )

23. Either

What is meant by self-inductance of a coil? Obtain an
expression for the self-inductance of a long solenoid. 1+2=3
Or
What are diamagnetic and ferromagnetic substances?
Write about the magnetic susceptibility of diamagnetic
and ferromagnetic substances. 1+1+½+½=3

24. Draw a labelled ray diagram to show the image formation
at least distance of distinct vision due to a compound
microscope and hence obtain an expression for its
magnifying power. 1+2=3

25. Either

Define the term ‘threshold frequency’ in relation to
photoelectric effect. Explain the variation of photoelectric
current with (a) the intensity of incident radiation and
(b) the frequency of incident radiation. 1+1+1=3
Or
Using the postulates of Bohr’s atomic model, find an
expression for the radius of the nth stationary orbit of
hydrogen atom. 3

26. Calculate the binding energy per nucleon for 30 Zn 64 in
MeV. (Take 1 a.m.u. = 931 MeV)
Given,
m p = 1·007825 a.m.u., m n = 1·008665 a.m.u.,
mass of 30 Zn 64 = 63·9423 a.m.u. 3

HS/XII/Sc/Ph/25/229 [ P.T.O.

( 10 )

27. Either

What is an optical fibre? Explain the principle of its
working. Mention two of its applications. 1+1+1=3
Or
Find an expression for the combine focal length of two
thin coaxial convex lenses placed in contact. 3

28. What is a rectifier? With the help of a labelled circuit
diagram, explain half-wave rectification using semi-
conductor diode. 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 dipole moment of an electric dipole? What is the
net charge on an electric dipole? State SI unit of dipole
moment of an electric dipole. Derive an expression for the
electric field intensity at a point on the equatorial line of
an electric dipole. 1+1+3=5
Or
Two point charges - q and + q separated by a short
distance 2a are placed in free space at points A and B
respectively. Derive an expression for the electric potential
at a point P whose distance from the centre O of the
line AB is r andrOP makes an angle q, with the electric
dipole moment p. Hence find the potential if P lies on
(a) axial line and (b) equatorial line. 3+1+1=5

HS/XII/Sc/Ph/25/229 [ Contd.

( 11 )

30. Either

State Biot-Savart law. Using this law, find an expression
for the magnetic field at a point P which is at a distance x,
on the axis of a circular current-carrying loop of radius R.
Also find the magnetic field if point P lies at the centre of
the loop. 1+3+1=5
Or
An AC voltage v = v 0 sin wt is applied across a pure
inductor of inductance L. Show mathematically that the
current flowing through it lags behind the applied voltage
by a phase angle of p /2. Explain the term ‘inductive
reactance’ and show that a pure inductor acts as a
conductor for DC. 3+1+1=5

31. Either

Derive lens maker formula for a thin convex lens. 5
Or
State Huygens’ principle for wave theory of light. Using
Huygens’ principle, derive the laws of reflection for plane
waves. 2+3=5

HHH

HS/XII/Sc/Ph/25/229 K25—5620

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