# Physics Shaalaa.com Model Set 2 2020-2021 HSC Science (General) 12th Board Exam Question Paper Solution

Physics [Shaalaa.com Model Set 2]
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

A diver in a swimming pool bends his head before diving. It ______

Increases his linear velocity

Decreases his angular velocity

Increases his moment of inertia

Decreases his moment of inertia

Concept: Moment of Inertia as an Analogous Quantity for Mass
Chapter: [0.01] Rotational Dynamics
[1] 1.ii

The average energy per molecule is proportional to ______

the pressure of the gas

the volume of the gas

the absolute temperature of the gas

the mass of the gas

Concept: Gases and Its Characteristics
Chapter: [0.03] Kinetic Theory of Gases and Radiation
[1] 1.iii

Heating a gas in a constant volume container is an example of which process?

isochoric

isobaric

cyclic

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

A set of tuning forks is arranged in ascending order of frequencies each tuning fork gives 8 beats/s with the preceding one. If the frequency of the first tuning fork is 120 Hz and the last fork is 200 Hz, then the number of tuning forks arranged will be, ______

8

9

10

11

Concept: Superposition of Waves
Chapter: [0.06] Superposition of Waves [0.06] Superposition of Waves
[1] 1.v

If an electron of charge (-e) and mass me revolves around the nucleus of an atom having an orbital magnetic moment m0, then the angular momentum of the electron is ______

L = (m_0e)/(2m_e)

L = e/(2m_0m_e)

L = (2m_0m_e)/e

L = (2e)/(m_0m_e)

Concept: Magnetic Materials
Chapter: [0.11] Magnetic Materials
[1] 1.vi

According to De-Broglie, the waves are associated with ______

moving neutral particles only.

moving charged particle only.

electrons only

all moving matter particles

Concept: De Broglie Hypothesis
Chapter: [0.14] Dual Nature of Radiation and Matter
[1] 1.vii

In a Bipolar junction transistor, the largest current flows through ______

in the emitter

in the collector

in the base

through CB junction

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

The moment of inertia of a circular loop of radius R, at a distance of R/2 around a rotating axis parallel to horizontal diameter of the loop is ______

½ MR

¾ MR

MR

2MR

Concept: Moment of Inertia as an Analogous Quantity for Mass
Chapter: [0.01] Rotational Dynamics
[1] 1.ix

Multiple Choice Question.

The energy stored in a soap bubble of diameter 6 cm and T = 0.04 N/m is nearly

0.9 × 10-3 J

0.4 × 10-3

0.7 × 10-3

0.5 × 10-3

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

The speed of electron having de Broglie wavelength of 10 -10 m is ______
(me = 9.1 × 10-31 kg, h = 6.63 × 10-34 J-s)

7.28 × 106 m/s

4 × 106 m/s

8 × 105 m/s

5.25 × 105 m/s

Concept: Bohr’s Atomic Model
Chapter: [0.15] Structure of Atoms and Nuclei
[8] 2 | Answer the following:
[1] 2.i

On what, the values of absorption coefficient, reflection coefficient, and transmission coefficient depend, in addition to the material of the object on which the radiation is an incident?

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

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

What is the net weight of a body when it falls with terminal velocity through a viscous medium?

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

What is the energy associated with the random, disordered motion of the molecules of a system called as?

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

What is the shape of the wavefront on Earth for Sunlight?

Concept: Reflection of Light at a Plane Surface
Chapter: [0.07] Wave Optics
[1] 2.vi

What is the angular momentum of an electron in the first excited state for a hydrogen atom?

Concept: Structure of Atoms and Nuclei
Chapter: [0.15] Structure of Atoms and Nuclei
[1] 2.vii
[1] 2.viii

A solenoid of length 50 cm of the inner radius of 1 cm and is made up of 500 turns of copper wire for a current of 5 A in it. What will be the magnitude of the magnetic field inside the solenoid?

Concept: Magnetic Field of a Solenoid and a Toroid
Chapter: [0.1] Magnetic Fields Due to Electric Current
Section B
[2] 3 | Attempt Any Eight:

Derive an expression for maximum safety speed with which a vehicle should move along a curved horizontal road. State the significance of it.

Concept: Rotational Dynamics
Chapter: [0.01] Rotational Dynamics
[2] 4

For a stationary wave set up in a string having both ends fixed, what is the ratio of the fundamental frequency to the third harmonic?

Concept: Stationary Waves
Chapter: [0.06] Superposition of Waves
[2] 5

How the frequency of the vibrating wire is affected if the load is fully immersed in water?

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
[2] 6

What are the disadvantages of a potentiometer over a voltmeter?

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
[2] 7

Distinguish between an ammeter and a voltmeter.

Concept: Current Electricity
Chapter: [0.09] Current Electricity
[2] 8

Define magnetization. State its SI unit and dimensions.

Concept: Magnetization and Magnetic Intensity
Chapter: [0.11] Magnetic Materials
[2] 9

Draw a neat labelled circuit diagram of a full-wave rectifier using a semiconductor diode.

Concept: p-n Junction Diode as a Rectifier
Chapter: [0.16] Semiconductor Devices
[2] 10

3 mole of a gas at temperature 400 K expands isothermally from an initial volume of 4 litres to a final volume of 8 litres. Find the work done by the gas. (R = 8.31 J mol-1 K-1)

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
[2] 11

The acceleration due to gravity on the surface of the moon is 1.7 m/s2. What is the time period of a simple pendulum on the surface of the moon if its time period on the surface of the earth is 3.5 s? (g on the surface of earth = 9.8 m/s2

Concept: Amplitude (A), Period (T) and Frequency (N) of S.H.M.
Chapter: [0.05] Oscillations
[2] 12

Currents of equal magnitude pass through two long parallel wires having a separation of 1.35 cm. If the force per unit length on each of the wires is 4.76 x 10-2 N/m, what is I?

Concept: Magnetic Field Produced by a Current in a Circular Arc of a Wire
Chapter: [0.1] Magnetic Fields Due to Electric Current
[2] 13

If the total energy of radiation of frequency 1014 Hz is 6.63 J, Calculate the number of photons in the radiation.

Concept: The Photoelectric Effect
Chapter: [0.14] Dual Nature of Radiation and Matter
[2] 14

Draw the circuit symbol for NPN and PNP transistors. What is the difference in the Emitter, Base, and Collector regions of a transistor?

Concept: Bipolar Junction Transistor (BJT)
Chapter: [0.16] Semiconductor Devices
Section C
[3] 15 | Attempt Any Eight:

State Stoke’s law and give two factors affecting angle of contact.

Concept: Stokes’ Law
Chapter: [0.02] Mechanical Properties of Fluids
[3] 16

Obtain the expression for the period of a magnet vibrating in a uniform magnetic field and performing S.H.M.

Concept: Oscillations
Chapter: [0.05] Oscillations
[3] 17

Explain experimental setup for Fraunhofer diffraction with neat diagram.

Concept: Diffraction of Light
Chapter: [0.07] Wave Optics
[3] 18

Explain step up and step down transformer?

Concept: Transformers
Chapter: [0.12] Electromagnetic Induction [0.16] Electromagnetic Inductions
[3] 19

Obtain an expression for the energy stored in a charged condenser. Express it in different forms.

Concept: Capacitors and Capacitance, Combination of Capacitors in Series and Parallel
Chapter: [0.08] Electrostatics
[3] 20

Explain Biot Savart's Law.

Concept: Magnetic Field Due to a Current: Biot-savart Law
Chapter: [0.1] Magnetic Fields Due to Electric Current
[3] 21

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

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

A radio can tune over the frequency range of a portion of the MW broadcast band (800kHz -1200kHz). If its LC circuit has an effective inductance of 200mH, what must be the range of its variable condenser?

Concept: LC Oscillations
Chapter: [0.13] AC Circuits [0.16] Electromagnetic Inductions
[3] 23

In Fraunhoffer diffraction by a narrow slit, a screen is placed at a distance of 2 m from the lens to obtain the diffraction pattern. If the slit width is 0.2 mm and the first minimum is 5 mm on either side of the central maximum, find the wavelength of light.

Concept: Diffraction of Light
Chapter: [0.07] Wave Optics
[3] 24

Two parallel plate capacitors X and Y have the same area of the plates and the same separation between them is connected in series to a battery of 15 V. X has air between the plates while Y contains a dielectric of constant k = 2.

i) Calculate the capacitance of each capacitor if the equivalent capacitance of the combination is 2 μF.

ii) Calculate the potential difference between the plates of X and Y.

iii) What is the ratio of the electrostatic energy stored in X and Y?

Concept: Capacitors and Capacitance, Combination of Capacitors in Series and Parallel
Chapter: [0.08] Electrostatics
[3] 25

A cylinder containing one gram molecule of the gas was compressed adiabatically until its temperature rose from 27°C to 97°C. Calculate the work done and heat produced in the gas (𝛾 = 1.5).

Concept: Heat, Internal Energy and Work
Chapter: [0.04] Thermodynamics
[3] 26

A flywheel of mass 8 kg and radius 10 cm rotating with a uniform angular speed of 5 rad/sec about its axis of rotation, is subjected to an accelerating torque of 0.01 Nm for 10 seconds. Calculate the change in its angular momentum and change in its kinetic energy.

Concept: Angular Momentum or Moment of Linear Momentum
Chapter: [0.01] Rotational Dynamics
Section D
[4] 27 | Attempt Any Three:
[2] 27.i

Derive Laplace’s law for spherical membrane of bubble due to surface tension.

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[2] 27.ii

Show that half life period of radioactive material varies inversely to decay constant λ.

Chapter: [0.15] Structure of Atoms and Nuclei
[4] 28

Derive Mayer’s relation.

Concept: Specific Heat Capacity
Chapter: [0.03] Kinetic Theory of Gases and Radiation
[4] 29
[2] 29.i

Distinguish between a potentiometer and a voltmeter.

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
[2] 29.ii

An iron rod of the area of cross-section 0.1m2 is subjected to a magnetizing field of 1000 A/m. Calculate the magnetic permeability of the iron rod. [Magnetic susceptibility of iron = 59.9, magnetic permeability of vacuum = 4π x 10-7 S. I. unit]

Concept: Magnetic Properties of Materials
Chapter: [0.11] Magnetic Materials [0.15] Magnetism
[4] 30
[2] 30.i

Why and where are eddy currents are undesirable? How are they minimized?

Concept: Eddy Currents
Chapter: [0.12] Electromagnetic Induction
[2] 30.ii

Calculate De Broglie's wavelength of the bullet moving with speed 90m/sec and having a mass of 5 gm.

Concept: De Broglie Hypothesis
Chapter: [0.14] Dual Nature of Radiation and Matter
[4] 31
[2] 31.i

Obtain an expression for the self-inductance of a solenoid.

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

The angular momentum of an electron in the 3rd Bohr orbit of a Hydrogen atom is 3.165 × 10-34 kg m2/s. Calculate Plank’s constant h.

Concept: Bohr’s Atomic Model
Chapter: [0.15] Structure of Atoms and Nuclei

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