# Physics Shaalaa.com Model Set 3 2020-2021 HSC Science (General) 12th Board Exam Question Paper Solution

Physics [Shaalaa.com Model Set 3]
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
 1 | Select and write the correct answer:
 1.i

Acceleration of a particle executing S.H.M. at its mean position.

Is infinity

Varies

Is maximum

Is zero

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

Which of the following cannot produce two coherent sources?

Lloyd’s mirror

Fresnel biprism

Young’s double-slit

Prism

Concept: Introduction of Wave Optics
Chapter: [0.07] Wave Optics
 1.iii

Light follows wave nature because ______

Light rays travel in a straight line

Light exhibits the phenomenon of reflection and refraction

Light exhibits the phenomenon of interference

Light causes the phenomenon of the photoelectric effect

Concept: Introduction of Wave Optics
Chapter: [0.07] Wave Optics
 1.iv

If an electron is brought towards another electron, the electric potential energy of the system ______

decreases

increases

Becomes zero

Remains same

Concept: Electric Potential and Potential Energy
Chapter: [0.08] Electrostatics
 1.v

Relative permeability of iron 5500, then its magnetic susceptibility will be ______

5500 × 107

5501

5499

5500 × 10-7

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

According to the right-hand rule, the direction of magnetic induction if the current is directed in an anticlockwise direction is ______

perpendicular and inwards

perpendicular and outwards

same as current

opposite to that of current

Concept: Magnetic Force
Chapter: [0.1] Magnetic Fields Due to Electric Current
 1.vii

Choose the correct option.

Solar cell operates on the principle of:

diffusion

recombination

photovoltaic action

carrier flow

Concept: Special Purpose Junction Diodes
Chapter: [0.16] Semiconductor Devices
 1.viii

In a common base configuration, the transistor has an emitter current of 10 mA and a collector current of 9.8 mA. The value of base current is ______

0.1 mA

0.2 mA

0.3 mA

0.4 mA

Concept: Bipolar Junction Transistor (BJT)
Chapter: [0.16] Semiconductor Devices
 1.ix

An electric bulb operates 10 V d.c. If this bulb is connected to an a.c. source and gives normal brightness, then the peak value of the source is ______

141.4 V

14.14 V

1.414 V

0.1414 V

Concept: AC Circuits
Chapter: [0.13] AC Circuits
 1.x

In the expression e = –dΦ/dt, the -ve sign signifies ______

The induced emf is produced only when magnetic flux decreases

The induced emf opposes the change in the magnetic flux

The induced emf is opposite to the direction of the flux.

The induced emf is independent of change in magnetic flux.

Concept: Induced Emf in a Stationary Coil in a Changing Magnetic Field
Chapter: [0.12] Electromagnetic Induction
 2 | Answer the following:
 2.i

What is the surface film?

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

Why wave motion is doubly periodic?

Concept: Superposition of Waves
Chapter: [0.06] Superposition of Waves [0.06] Superposition of Waves
 2.iii

What are harmonics?

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

A group of objects that can form a unit which may have the ability to exchange energy with its surrounding is called what?

Concept: Thermodynamics
Chapter: [0.04] Thermodynamics
 2.v

In Young’s double-slit experiment, if there is no initial phase difference between the light from the two slits, a point on the screen corresponds to the 5th minimum. What is the path difference?

Concept: Nature of Light
Chapter: [0.07] Wave Optics
 2.vi

Which physical quantity has its unit as J/C? Is it a scalar or vector?

Concept: Electric Potential and Potential Energy
Chapter: [0.08] Electrostatics
 2.vii

The relative velocity between two parallel layers of water is 8 cm/s and the perpendicular distance between them is 0.1 cm. Calculate the velocity gradient.

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

The radius of the smallest orbit of the electron( aO) in a hydrogen atom is 0.053 nm. What is the radius of the 4th orbit of the electron in a hydrogen atom?

Concept: Structure of Atoms and Nuclei
Chapter: [0.15] Structure of Atoms and Nuclei
Section B
 3 | Attempt Any Eight:

State the assumptions made for thermodynamic processes.

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
 4

Obtain the differential equation of linear simple harmonic motion.

Concept: Differential Equation of Linear S.H.M.
Chapter: [0.04] Oscillations [0.05] Oscillations
 5

State any two laws of the simple pendulum.

Concept: Simple Pendulum
Chapter: [0.05] Oscillations
 6

Show the graphical representation of radiant power of a black body per unit range of wavelength as a function of wavelength.

Concept: Perfect Blackbody
Chapter: [0.03] Kinetic Theory of Gases and Radiation
 7

Draw a neat labeled diagram of Ferry’s black body.

Concept: Perfect Blackbody
Chapter: [0.03] Kinetic Theory of Gases and Radiation
 8

State any four applications of beats.

Concept: Beats
Chapter: [0.06] Superposition of Waves [0.07] Wave Motion [0.1] Wave Theory of Light
 9

Define: Ionization energy.

Concept: Structure of Atoms and Nuclei
Chapter: [0.15] Structure of Atoms and Nuclei
 10

A raindrop of radius 0.3 mm falls through the air with a terminal velocity of 1 m/s. The viscosity of air is 18 x 10-6 N-s /m2. Find the viscous force on the raindrop.

Concept: Critical Velocity and Reynolds Number
Chapter: [0.02] Mechanical Properties of Fluids
 11

The optical path of a ray of light of a given wavelength travelling a distance of 3 cm in flint glass having refractive index 1.6 is the same as that on travelling a distance x cm through a medium having a refractive index 1.25. Determine the value of x.

Concept: Introduction of Wave Optics
Chapter: [0.07] Wave Optics
 12

A Plane Wavefront of light of wavelength 5500 A.U. is incident on two slits in a screen perpendicular to the direction of light rays. If the total separation of 10 bright fringes on a screen 2 m away is 2 cm. Find the distance between the slits.

Concept: Introduction of Wave Optics
Chapter: [0.07] Wave Optics
 13

Explain De Broglie’s Hypothesis.

Concept: De Broglie Hypothesis
Chapter: [0.14] Dual Nature of Radiation and Matter
 14

A sonometer wire of length 1 m is stretched by a weight of 10 kg. The fundamental frequency of vibration is 100 Hz. Determine the linear density of the material of the wire.

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
Section C
 15 | Attempt Any Eight:

Derive an expression for the difference in tensions at the highest and lowest point for a particle performing the vertical circular motion.

Concept: Vertical Circular Motion
Chapter: [0.01] Rotational Dynamics
 16

Obtain an expression for the capillary rise or fall using the forces method.

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

Calculate the ratio of two specific heats of polyatomic gas molecules.

Concept: Specific Heat Capacity
Chapter: [0.03] Kinetic Theory of Gases and Radiation
 18

What is a potential gradient? How is it measured? Explain.

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
 19

Explain with a neat circuit diagram. How you will determine the unknown resistances using a meter bridge.

Concept: Wheatstone Bridge
Chapter: [0.09] Current Electricity [0.13] Current Electricity
 20

Determine the motional emf induced in a straight conductor moving in a uniform magnetic field with constant velocity on the basis of Lorentz force.

Concept: Induced Emf in a Stationary Coil in a Changing Magnetic Field
Chapter: [0.12] Electromagnetic Induction
 21

What is a logic gate? Draw the symbol and give the truth table for NOT gate. Why NOT the gate is called an inverter?

Concept: Logic Gates
Chapter: [0.16] Semiconductor Devices
 22

The magnetic field at the centre of a circular loop of radius 12.3 cm is 6.4 x 10-6 T. What will be the magnetic moment of the loop?

Concept: Magnetic Lines for a Current Loop
Chapter: [0.1] Magnetic Fields Due to Electric Current
 23

A plane of a coil of 10 turns is tightly wound around a solenoid of diameter 2 cm having 400 turns per centimeter. The relative permeability of the core is 800. Calculate the inductance of the solenoid.

Concept: Induction and Energy Transfer
Chapter: [0.12] Electromagnetic Induction
 24

What is the capacitive reactance of a capacitor of 5µF at a frequency of (1) 50 Hz and (2) 20KHZ?

Concept: AC Circuits
Chapter: [0.13] AC Circuits
 25

The energy of a photon is 2 eV. Find its frequency and wavelength.

Concept: The Photoelectric Effect
Chapter: [0.14] Dual Nature of Radiation and Matter
 26

A radioactive substance decays to (1/10)th of its original value in 56 days. Calculate its decay constant.

Chapter: [0.15] Structure of Atoms and Nuclei
Section D
 27 | Attempt Any Three:

What is a conical pendulum? Obtain an expression for its time period

Concept: Rotational Dynamics
Chapter: [0.01] Rotational Dynamics
 28

Explain the thermodynamics of the isobaric process.

Concept: Thermodynamic Process
Chapter: [0.04] Thermodynamics
 29
 29.i

Explain the principle of a capacitor.

Concept: Capacitors and Capacitance, Combination of Capacitors in Series and Parallel
Chapter: [0.08] Electrostatics
 29.ii

Three-point charges +q, +2q and Q are placed at the three vertices of an equilateral triangle. Find the value of charge Q (in terms of q), so that the electric potential energy of the system is zero.

Concept: Electric Potential and Potential Energy
Chapter: [0.08] Electrostatics
 30
 30.i

A solenoid has a core of material with relative permeability 500 and its windings carry a current of 1 A. The number of turns of the solenoid is 500 per meter. Calculate the magnetization of the material.

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

A solenoid of length π m and 5 cm in diameter has a winding of 1000 turns and carries a current of 5 A. Calculate the magnetic field at its centre along the radius.

Concept: Magnetic Field of a Solenoid and a Toroid
Chapter: [0.1] Magnetic Fields Due to Electric Current
 31
 31.i

State any two characteristics of a series LCR AC resonance circuit.

Concept: Electric Resonance
Chapter: [0.13] AC Circuits
 31.ii

A magnet of magnetic moment 3Am2 weighs 75 g. The density of the material of the magnet is 7500 kg/m3. what is magnetization?

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

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