# Physics Shaalaa.com Model Set 1 2020-2021 HSC Science (General) 12th Board Exam Question Paper Solution

Physics [Shaalaa.com Model Set 1]
Date: April 2021
Duration: 3h
1. The question paper is divided into four sections.
2. Section A: Q. No. 1 contains Ten multiple-choice type of questions carrying One mark each.
3. Section A: Q. No. 2 contains Eight very short answer type of questions carrying One mark each.
4. Section B: Q. No. 3 to Q. No. 14 contains Twelve short answer type of questions carrying Two marks each. (Attempt any Eight).
5. Section C: Q. No.15 to Q. No. 26 contains Twelve short answer type of questions carrying Three marks each. (Attempt any Eight).
6. Section D: Q.No. 27 to Q. No. 31 contains Five long answer type of questions carrying Four marks each. (Attempt any Three).
7. Use of log table is allowed. Use of calculator is not allowed.
8. Figures to the right indicate full marks.
9. For each MCQ, correct answer must be written along with its alphabet.
e.g., (a) ..... / (b ) .... / ( c ) .... / ( d) ..... Only first attempt will be considered for evaluation.
10. Physical constants:
a. Latent heat of vaporisation, Lvap = 2256 kJ/kg
b. Acceleration due to gravity, g = 9.8 m/s2

Section A
[10] 1 | Select and write the correct answer:
[1] 1.i

Which of the following is correct, when the energy is transferred to a system from its environment?

System gains energy

System loses energy

System releases energy

the system does not exchange energy

Concept: Heat, Internal Energy and Work
Chapter: [0.04] Thermodynamics
[1] 1.ii

For work done to be reversible, the process should be ______

cyclic

isobaric

isochoric

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
[1] 1.iii

A particle is performing simple harmonic motion with amplitude A and angular velocity ω. the ratio of maximum velocity to maximum acceleration is ______

ω

I/ω

ω2

A/ω

Concept: Acceleration (a), Velocity (v) and Displacement (x) of S.H.M.
Chapter: [0.05] Oscillations
[1] 1.iv

In the law of tension, the fundamental frequency of the vibrating string is, ______

inversely proportional to the square root of tension

directly proportional to the square of tension

directly proportional to the square root of tension

inversely proportional to the density

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
[1] 1.v

The integral multiple of fundamental frequencies are ______

beats

resonance

overtones

harmonics

Concept: Harmonics and Overtones
Chapter: [0.06] Superposition of Waves
[1] 1.vi

A LED emits visible white light when its ______

junction is reversed biased

depletion layer widens

holes and electrons recombine

junction becomes hot

Concept: Semiconductor Devices
Chapter: [0.16] Semiconductor Devices
[1] 1.vii

Insect moves over the surface of water because of ______

Elasticity

Surface tension

Friction

Viscosity

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[1] 1.viii

Two capillary tubes of radii 0.6 cm and 0.3 cm are dipped in the same liquid. The ratio of heights through which the liquid will rise in the tubes is ______

2:1

1:2

4:1

1:4

Concept: Fluid and Its Properties
Chapter: [0.02] Mechanical Properties of Fluids
[1] 1.ix

Light of wavelength 5000 A.U. falls on a plane reflecting surface. The frequency of reflected light is ______

6 × 1014Hz

5 × 1014Hz

2 × 1014Hz

1.666 × 1014Hz

Concept: Nature of Light
Chapter: [0.07] Wave Optics
[1] 1.x

You are given a number of capacitors labelled as 8μF - 250V. Find the number of capacitors needed to get an arrangement equivalent to 16μF - 1000V.

4

16

32

64

Concept: Capacitors and Capacitance, Combination of Capacitors in Series and Parallel
Chapter: [0.08] Electrostatics
[8] 2 | Answer the following:
[1] 2.i

What are cohesive forces?

Concept: Fluid and Its Properties
Chapter: [0.02] Mechanical Properties of Fluids
[1] 2.ii

Under which condition laws of Boyle, Charles, and Gay-Lussac are valid?

Concept: Interpretation of Temperature in Kinetic Theory
Chapter: [0.03] Kinetic Theory of Gases and Radiation
[1] 2.iii

When two objects are said to be in thermal equilibrium?

Concept: Thermal Equilibrium
Chapter: [0.04] Thermodynamics [0.09] Kinetic Theory of Gases and Radiation
[1] 2.iv

A simple pendulum moves from one end to the other in ¼ second. What is its frequency?

Concept: Amplitude (A), Period (T) and Frequency (N) of S.H.M.
Chapter: [0.05] Oscillations
[1] 2.v

What is the basis of Kirchhoff’s current law and voltage law?

Concept: Kirchhoff’s Laws of Electrical Network
Chapter: [0.09] Current Electricity
[1] 2.vi

What does the ratio of magnetization to magnetic intensity indicate?

Concept: Magnetization and Magnetic Intensity
Chapter: [0.11] Magnetic Materials
[1] 2.vii

A square metal plate of area 100 cm2 moves parallel to another plate with a velocity of 10 cm/s, both plates immersed in water. If the viscous force is 200 dyne and the viscosity of water is 0.01 poise, what is the distance between them?

Concept: Critical Velocity and Reynolds Number
Chapter: [0.02] Mechanical Properties of Fluids
[1] 2.viii

What do you mean by dielectric polarization?

Concept: Dielectrics and Electric Polarisation
Chapter: [0.08] Electrostatics
Section B
[2] 3 | Attempt Any Eight:

A flywheel is revolving with a constant angular velocity. A chip of its rim breaks and flies away. What will be the effect on its angular velocity?

Concept: Angular Momentum or Moment of Linear Momentum
Chapter: [0.01] Rotational Dynamics
[2] 4

Draw a p-V diagram of the reversible process.

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
[2] 5

Draw a p-V diagram showing negative work with varying pressure.

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
[2] 6

Distinguish between an overtone and harmonic.

Concept: Harmonics and Overtones
Chapter: [0.06] Superposition of Waves
[2] 7

What are stationary waves? Why are they called stationary waves?

Concept: Stationary Waves
Chapter: [0.06] Superposition of Waves
[2] 8

Draw a neat labelled diagram of a schematic of the experimental setup for the photoelectric effect.

Concept: The Photoelectric Effect
Chapter: [0.14] Dual Nature of Radiation and Matter
[2] 9

Concept: Special Purpose Junction Diodes
Chapter: [0.16] Semiconductor Devices
[2] 10

The moment of inertia of a body about a given axis is 1.2 kgm2. initially, the body is at rest. For what duration on the angular acceleration of 25 radian/sec2 must be applied about that axis in order to produce rotational kinetic energy of 1500 joule?

Concept: Moment of Inertia as an Analogous Quantity for Mass
Chapter: [0.01] Rotational Dynamics
[2] 11

1000 calories of radiant heat are incident on a body. If the body absorbs 400 calories of heat, find the coefficient of emission of the body.

Chapter: [0.03] Kinetic Theory of Gases and Radiation
[2] 12

Four resistances 6Ω, 6Ω, 6Ω and 18Ω form a Wheatstone bridge. Find the resistance which connected across the 18Ω resistance will balance the network.

Concept: Wheatstone Bridge
Chapter: [0.09] Current Electricity [0.13] Current Electricity
[2] 13

The magnetic flux through a loop varies according to the relation Φ = 8t2 + 6t + 2, Φ is in milliweber and t is in second. What is the magnitude of the induced emf in the loop at t = 2 seconds?

Concept: Induced Emf in a Stationary Coil in a Changing Magnetic Field
Chapter: [0.12] Electromagnetic Induction
[2] 14

Define current amplification factor αDC and βDC Obtain the relation between them.

Concept: Semiconductor Devices
Chapter: [0.16] Semiconductor Devices
Section C
[3] 15 | Attempt Any Eight:

Derive an expression for the kinetic energy of a rotating body with uniform angular velocity.

Concept: Rotational Dynamics
Chapter: [0.01] Rotational Dynamics
[3] 16

Explain the phenomena of surface tension on the basis of molecular theory.

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[3] 17

Obtain an expression for the resultant amplitude of, the composition of two S.H.M.’s having the same period along the same path.

Concept: Amplitude (A), Period (T) and Frequency (N) of S.H.M.
Chapter: [0.05] Oscillations
[3] 18

Explain the reflection of light at a plane surface with the help of a neat ray diagram.

Concept: Reflection of Light at a Plane Surface
Chapter: [0.07] Wave Optics
[3] 19

Describe Young’s double-slit experiment with a neat diagram showing points of maximum and minimum intensity.

Concept: Resolving Power
Chapter: [0.07] Wave Optics
[3] 20

Explain the construction and working of the Moving coil Galvanometer.

Concept: Magnetic Fields Due to Electric Current
Chapter: [0.1] Magnetic Fields Due to Electric Current
[3] 21

Explain the term inductive reactance. State its unit and dimensions.

Concept: AC Circuits
Chapter: [0.13] AC Circuits
[3] 22

An alternating emf of 230V, 50Hz is connected across a pure ohmic resistance of 50Ω. Find (1) the current (2) equations for instantaneous values of current and voltage.

Concept: Phasors
Chapter: [0.13] AC Circuits
[3] 23

The work function of a surface is 3.1 eV. A photon of frequency 1 × 1015 Hz. Is an incident on it. Calculate the incident wavelength is photoelectric emission occurs or not.

Concept: The Photoelectric Effect
Chapter: [0.14] Dual Nature of Radiation and Matter
[3] 24

The primary of a transformer has 40 turns and works on 100 V and 100 W. Find a number of turns in the secondary to step up the voltage to 400 V. Also calculate the current in the secondary and primary.

Concept: Transformers
Chapter: [0.12] Electromagnetic Induction [0.16] Electromagnetic Inductions
[3] 25

A circular loop of radius 9.7 cm carries a current 2.3 A. Obtain the magnitude of the magnetic field
(a) at the centre of the loop
(b) at a distance of 9.7 cm from the centre of the loop but on the axis.

Concept: Magnetic Lines for a Current Loop
Chapter: [0.1] Magnetic Fields Due to Electric Current
[3] 26

A cell of e.m.f 1.5V and negligible internal resistance is connected in series with a potential meter of length 10 m and the total resistance of 20 Ω. What resistance should be introduced in the resistance box such that the potential drop across the potentiometer is one microvolt per cm of the wire?

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
Section D
[4] 27 | Attempt Any Three:

Explain the spectral distribution of blackbody radiation.

Concept: Spectral Distribution of Blackbody Radiation
Chapter: [0.03] Kinetic Theory of Gases and Radiation
[4] 28

State the postulates of Bohr’s atomic model. Hence show the energy of electrons varies inversely to the square of the principal quantum number.

Concept: Bohr’s Atomic Model
Chapter: [0.15] Structure of Atoms and Nuclei
[4] 29
[2] 29.i

Draw a neat labelled diagram showing energy levels and transition between them for the hydrogen atoms.

Concept: Structure of Atoms and Nuclei
Chapter: [0.15] Structure of Atoms and Nuclei
[2] 29.ii

An electron in an atom is revolving around the nucleus in a circular orbit of a radius of 5.3 x 10-11 m, with a speed of 2 x 106 m/s. Find the resultant orbital magnetic moment and angular momentum of the electron. [e = 1.6 x 10-19 C, me= 9.1 x 10-31 kg]

Concept: Origin of Magnetism in Materials
Chapter: [0.11] Magnetic Materials
[4] 30
[2] 30.i

Define magnetization. State its SI unit and dimensions. Derive the relation between magnetic field intensity(H) and magnetization(M) for a magnetic material placed in a magnetic field.

Concept: Magnetization and Magnetic Intensity
Chapter: [0.11] Magnetic Materials
[2] 30.ii

Two capacitors each of capacity 2 μF are connected in parallel. This system is connected in series with the third capacitor of 12μF capacity. Find the equivalent capacity of the system.

Concept: Capacitors and Capacitance, Combination of Capacitors in Series and Parallel
Chapter: [0.08] Electrostatics
[4] 31
[2] 31.i

Using Ampere's law, obtain an expression for the magnetic induction near a current-carrying straight infinitely long wire.

Concept: Electromagnetic Induction
Chapter: [0.12] Electromagnetic Induction [0.16] Electromagnetic Inductions
[2] 31.ii

Two spheres A and B of radius a and b respectively are at the same potential. Find the ratio of the surface charge densities of A and B.

Concept: Conductors and Insulators, Free Charges and Bound Charges Inside a Conductor
Chapter: [0.08] Electrostatics

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