PHYSICS BYTES

HP BOARD FINAL QUESTION PAPER 2025 (SERIES B)

Subject: PHYSICS (Theory) | Class: XII

GENERAL INSTRUCTIONS:

  • There are 27 questions in all. All questions are compulsory.
  • This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
  • Use of calculators is not allowed.

SECTION - A

(Multiple Choice Questions)

1.
Dimensions of absolute permittivity of free space $(\epsilon_{0})$ is:
(a) $M^{-1}L^{-3}T^{4}A^{2}$
(b) $M^{1}L^{3}T^{-4}A^{-2}$
(c) $M~L^{-3}T^{-4}A^{2}$
(d) $M^{-1}L^{3}T^{-4}A^{2}$
1
2.
Three Copper wires of lengths and cross-sectional areas are $(l,A)$, $(2l,A/2)$ and $(l/2,2A)$. The resistance is minimum in:
(a) wire of cross-sectional area $A/2$
(b) wire of cross-sectional area A
(c) wire of cross-sectional area 2A
(d) same in all the three cases.
1
3.
Antiparallel currents in two long parallel conductors are:
(a) attract each other
(b) repel each other
(c) neither attract nor repel each other
(d) attract and repel each other.
1
4.
A $15.0~\mu F$ capacitor is connected to a 220 V, 50 Hz source. The capacitive reactance will be:
(a) 222 $\Omega$
(b) 232 $\Omega$
(c) 212 $\Omega$
(d) 242 $\Omega$
1
5.
Lenz's law is the consequence of the law of conservation of:
(a) charge
(b) momentum
(c) mass
(d) energy
1
6.
Unpolarised light of intensity $(I_{0})$ passes through a single polaroid, the intensity of polarised light approximately is:
(a) $I_{0}$
(b) $2~I_{0}$
(c) $\frac{I_{0}}{4}$
(d) $\frac{I_{0}}{2}$
1
7.
An optician prescribes a corrective lens of power +2.5 D, then focal length of a convex lens is:
(a) +40 cm
(b) -40 cm
(c) +20 cm
(d) -20 cm
1
8.
In an experiment on photoelectric effect, the slope of cut-off voltage versus frequency of incident light is found to be $4.12\times10^{-15}V_{S}$. The value of Planck's constant is:
(a) $8.24\times10^{-34}Js$
(b) $13.18\times10^{-34}Js$
(c) $3.29\times10^{-34}Js$
(d) $6.59\times10^{-34}Js$
1
9.
Outside a nucleus:
(a) neutron is stable
(b) proton and neutron are stable
(c) neutron is unstable
(d) neither neutron nor proton is stable
1
10.
Trivalent acceptor atom doped in Tetravalent Lattice forms which type of semiconductor:
(a) p-type semiconductor
(b) n-type semiconductor
(c) Intrinsic semiconductor
(d) p-n semiconductor
1
For Q. No. 11 and 12, two statements are given - Assertion (A) and Reason (R). Choose:
(a) If both assertion and reason are true and reason is the correct explanation.
(b) If both assertion and reason are true but reason is not a correct explanation.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
11.
Assertion: A charge, whether stationary or in motion, produces a magnetic field.
Reason: Moving charges produce only electric field in the surrounding space.
1
12.
Assertion: Diodes can be used for rectifying an AC voltage.
Reason: A rectifier is used to convert alternating current into direct current.
1

SECTION - B

(Very Short Answer Type Questions)

13.
Define the term mobility of charge carriers in a conductor. What is the relation with relaxation time?
2
14.
What is meant by Magnetic intensity and intensity of Magnetisation?
2
15.
What are Photoelectric effect? Derive Einstein's photoelectric equation.
2
16.
A long straight wire carries a current of 35 A. What is the magnitude of the magnetic field at a point 20 cm from the wire?
OR
A Capacitor blocks d.c. but allows a.c. to pass through it. Explain, why?
2

SECTION - C

(Short Answer Type Questions)

17.
Draw a labelled diagram of an a.c. generator. Explain principle and construction of an a.c. generator.
3
18.
What is Interference? Obtain the conditions for constructive and destructive interference using Young's double slit experiment for interference of light.
3
19.
(a) What are Nuclear forces? State the four properties of Nuclear force.
(b) Convert one a.m.u into MeV.
3
20.
An electric dipole with dipole moment $4\times10^{-9}$ cm is aligned at $30^{\circ}$ with the direction of a uniform electric field of magnitude $5\times10^{4}NC^{-1}$. Calculate the magnitude of the torque acting on the dipole.
3
21.
What is displacement current? Write down four Maxwell's equations in electric and magnetic fields.
3
22.
What is Internal resistance of a cell? Prove that the Internal resistance of a cell, $r=(\frac{E}{V}-1)R$ Where E is the e.m.f. of the cell, V is the terminal potential difference and R is the external resistance used in circuit.
3
23.
(a) State the three postulates of Bohr's model in hydrogen atom.
(b) The ground state energy of Hydrogen atom is -13.6 eV. What are the Kinetic and potential energies of the electron in this state?
3

SECTION - D

(Case Study Based Question)

24.
Study the following paragraph and answer question numbers (A) to (D) based on it. An equipotential surface is a surface over which potential has a constant value. For a point charge, concentric spheres centred at a location of the charge on equipotential surfaces. The electric field E at a point is perpendicular to equipotential surface through the point. E is in the direction of the steepest decrease of the potential. Potential energy of two charges $q_{1}$, $q_{2}$ at $r_{1}$, $r_{2}$ is given by: $U=\frac{1}{4\pi\epsilon_{0}}\cdot\frac{q_{1}q_{2}}{r_{12}}$ where $r_{12}$ is the distance between $q_{1}$ and $q_{2}$. The potential energy of a charge q in an external potential $V(r)$ is $qV(r)$. The potential energy of a dipole moment p in a uniform electric field (E) is - P.E. Just outside the surface of a charged conductor, E is normal to the surface given by $E=\frac{\sigma}{\epsilon_{0}}\hat{n}$; where $\hat{n}$ is the unit vector along the outward normal to the surface and $\sigma$ is the surface charge density. In a cavity within a condutor, the electric field is zero.

(A) The angle between the electric lines of force and equipotential surface is:

(a) $0^{\circ}$
(b) $45^{\circ}$
(c) $90^{\circ}$
(d) $180^{\circ}$

(B) Electric potential (V) and electric flux ($\phi$) are:

(a) both vectors
(b) V is scalar, $\phi$ is vector
(c) V is vector, $\phi$ is scalar
(d) Both scalars.

(C) Equipotential surfaces at a great distance from a collection of charges whose total sum is not zero are approximately:

(a) Concentric spheres
(b) Parallel planes
(c) Concentric circles
(d) Parallel linear lines.

(D) A charge of 5 C moves between two plates maintained at a potential difference of 0.5 Volt. The energy acquired by the charge is:

(a) 2 J
(b) 2.5 J
(c) 3 J
(d) 3.5 J
4

SECTION - E

25.
What is a compound microscope? With the help of ray diagram, explain the working of compound microscope. Find an expression for its magnifying power. How can magnifying power be increased?
OR
(a) Double-Convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the Radius of curvature required if the focal length is to be 20 cm?
(b) A converging and a diverging lens of equal focal lengths are placed co-axially in contact. Find the focal length and power of the combination.
5
26.
(a) What is Rectifier? With the help of a circuit diagram, explain the use of a p-n junction diode as a full wave rectifier, giving its input and output waveforms.
(b) In half wave rectification, what is the output frequency, if the input frequency is 50 Hz? What is the output frequency of a full wave rectifier for the same input frequency?
5
27.
An a.c. voltage $E=E_{0} \sin\omega t$ is applied across a series combination of an inductor (L), a capacitor (C) and a resistor (R). Using the phasor diagram, derive an expression for impedance of LCR-circuit. Calculate the resonant frequency.
OR
Figure shows a series LCR-circuit connected to a variable frequency 230 V source. $L=5.0H$, $C=80~\mu F$, $R=40\Omega$. (i) Determine the source of frequency which drives the circuit in resonance.
(ii) Obtain the impedance of the circuit and the amplitude of the current at resonating frequency.
(iii) Determine the r.m.s potential drop across the three elements of the circuit.
5
View Solutions Key