HSC Science (Electronics) 12th Board ExamMaharashtra State Board
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# Question Paper Solutions - Physics 2016 - 2017 HSC Science (Electronics) 12th Board Exam

SubjectPhysics
Year2016 - 2017 (March)

Marks: 70
[7]1 | Select and write the most appropriate answer from the given alternatives for each sub-question:
[1]1.1

If the pressure of an ideal gas decreases by 10% isothermally, then its volume will _______.

(A) decrease by 9%

(B) increase by 7%

(C) increase by 10%

(D) increase by 11.4%

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Derivation for Pressure of a Gas
[1]1.2

Stretching of a rubber band results in _______.

(A) no change in potential energy.

(B) zero value of potential energy.

(C) increase in potential energy.

(D) decrease in potential energy.

Chapter: [5] Elasticity
Concept: Elastic Energy
[1]1.3

When the angular acceleration of a rotating body is zero, which physical quantity will be equal to zero?

(A) Angular momentum

(B) Moment of inertia

(C) Torque

Chapter: [1] Circular Motion
Concept: Angular Acceleration
[1]1.4

In a damped harmonic oscillator, periodic oscillations have _______ amplitude.

(B) suddenly increasing

(C) suddenly decreasing

Chapter: [4] Oscillations
Concept: Simple Harmonic Motion
[1]1.5

A sine wave of wavelength λ is travelling in a medium. What is the minimum distance between two particles of the medium which always have the same speed?

(A)lambda

(B)lambda/2

(C)lambda/3

(D)lambda/4

Chapter: [7] Wave Motion
Concept: Simple Harmonic Progressive Waves,
[1]1.6

Velocity of transverse wave along a stretched string is proportional to _______. (T = tension
in the string)

(A) sqrtT

(B)  T

(C) 1/sqrtT

(D) 1/T

Chapter: [5] Elasticity
Concept: Definition of Stress and Strain
[1]1.7

Find the wavelength at which a black body radiates maximum energy, if its temperature is 427°C.
(Wein’s constant b = 2.898 × 10-3 mK)

(A) 0.0414 × 10-6m

(B) 4.14 × 10-6m

(C) 41.4 × 10-6m

(D) 414 × 10-6m

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Qualitative Ideas of Blackbody Radiation
[12]2 | Attempt any six
[2]2.1

Explain the concept of centripetal force.

Chapter: [1] Circular Motion
Concept: Dynamics of Uniform Circular Motion - Centripetal Force
[2]2.2

Prove that root mean square velocity of gas molecule is directly proportional to the square root of its absolute temperature.

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Kinetic Theory of Gases- Assumptions
[2]2.3

Obtain the differential equation of linear simple harmonic motion.

Chapter: [4] Oscillations
Concept: Differential Equation of Linear S.H.M.
[2]2.4

Draw a neat, labelled diagram for a liquid surface in contact with a solid, when the angle of contact is acute.

Chapter: [6] Surface Tension
Concept: Capillarity and Capillary Action
[2]2.5

A hole is drilled half way to the centre of the Earth. A body is dropped into the hole. How much will it weigh at the bottom of the hole if the weight of the body on the Earth’s surface is 350 N?

Chapter: [2] Gravitation
Concept: Acceleration Due to Gravity and Its Variation with Altitude and Depth
[2]2.6

A solid sphere of mass 1 kg rolls on a table with linear speed 2 m/s, find its total kinetic energy.

Chapter: [3] Angular Momentum
Concept: Rolling Motion
[2]2.7

A transverse wave is produced on a stretched string 0.9 m long and fixed at its ends. Find the speed of the transverse wave, when the string vibrates while emitting second overtone of frequency 324 Hz.

Chapter: [7] Wave Motion
Concept: Reflection of Transverse and Longitudinal Waves
[2]2.8

A body cools at the rate of 0.5°C / minute when it is 25° C above the surroundings. Calculate the rate of cooling when it is 15°C above the same surroundings.

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Derivation of Boyle’s Law
[9]3 | Attempt any THREE
[3]3.1

Show that period of a satellite revolving around the Earth depends upon mass of the Earth.

Chapter: [2] Gravitation
Concept: Projection of Satellite
[3]3.2

Obtain an expression for torque acting on a rotating body with constant angular acceleration. Hence state the dimensions and SI unit of torque.

Chapter: [3] Angular Momentum
Concept: Torque and Angular Momentum
[3]3.3

The total energy of free surface of a liquid drop is 2π times the surface tension of the liquid. What is the diameter of the drop? (Assume all terms in SI unit).

Chapter: [6] Surface Tension
Concept: Surface Tension
[3]3.4

A vehicle is moving on a circular track whose surface is inclined towards the horizon at an angle of 10°. The maximum velocity with which it can move safely is 36 km / hr. Calculate the length of the circular track. [π = 3.142]

Chapter: [1] Circular Motion
Concept: Uniform Circular Motion
[7]4 | Attempt any one of the following
[7]4.1

Prove the law of conservation of energy for a particle performing simple harmonic motion.Hence graphically show the variation of kinetic energy and potential energy w. r. t.instantaneous displacement.

Chapter: [4] Oscillations
Concept: K.E.(Kinetic Energy) and P.E.(Potential Energy) in S.H.M.

Two sound notes have wavelengths 83/170 m and 83/172 m in the air. These notes when sounded together produce 8 beats per second. Calculate the velocity of sound in the air and frequencies of the two notes.

Chapter: [8] Stationary Waves
Concept: Study of Vibrations of Air Columns
[7]4.2

Explain analytically how the stationary waves are formed

Chapter: [8] Stationary Waves
Concept: Formation of Stationary Waves on String

Show the formation of stationary waves diagramatically

Chapter: [8] Stationary Waves
Concept: Formation of Stationary Waves on String

A mass of 1 kg is hung from a steel wire if radius 0.5 mm and length 4 m. Calculate the extension produced. What should be the area of cross-section of the wire so that elastic  limit is not exceeded? Change in radius is negligible

(Given : g = 9.8 m/s2; Elastic limit of steel is 2.4 x 108 N/m2;Y for steel (Ysteel) = 20 x 1010 N/m2; π = 3.142)

Chapter: [5] Elasticity
Concept: Behaviour of Metal Wire Under Increasing Load
[1]5 | Select and write the most appropriate answer from the given alternatives for each sub-question:
[1]5.1

If A.C. voltage is applied to a pure capacitor, then voltage across the capacitor ______.

(C) lags behind the current by phase angle (π/2) rad.
(D) lags behind the current by phase angle π rad.

Chapter: [16] Electromagnetic Inductions
Concept: Inductance and Capacitance
[1]5.2

In Doppler effect of light, the term “red shift” is used for ______.

(A) frequency increase

(B) frequency decrease

(C) wavelength decrease

(D) frequency and wavelength increase

Chapter: [7] Wave Motion
Concept: Beats

In Doppler effect of light, the term “red shift” is used for ______.

(A) frequency increase

(B) frequency decrease

(C) wavelength decrease

(D) frequency and wavelength increase

Chapter: [10] Wave Theory of Light
Concept: Beats
[1]5.3

If a watch-glass containing a small quantity of water is placed on two dissimilar magnetic poles, then water ______.

(A) shows a depression in the middle.

(B) shows an elevation in the middle.

(C) surface remains horizontal.

(D) evaporates immediately.

Chapter: [14] Magnetic Effects of Electric Current
Concept: Motion in Combined Electric and Magnetic Fields - Cyclotron
[1]5.4

Any device that converts one form of energy into another is termed as ______.

(A) amplifier

(B) transducer

(D) demodulator

Chapter: [20] Communication Systems
Concept: Elements of a Communication System
[1]5.5

When a p-n-p transistor is operated in saturation region, then its ______.

(A) base-emitter junction is forward biased and base-collector junction is reverse biased.
(B) both base-emitter and base-collector junctions are reverse biased.
(C) both base-emitter and base-collector junctions are forward biased.
(D) base-emitter junction is reverse biased and base-collector junction is forward biased

Chapter: [19] Semiconductors
Concept: Transistor and Characteristics of a Transistor
[1]5.6

In a photon-electron collision ______.
(A) only total energy is conserved.
(B) only total momentum is conserved.
(C) both total energy and total momentum are conserved.
(D) both total momentum and total energy are not conserved

Chapter: [18] Atoms, Molecules and Nuclei
Concept: Nuclear Energy - Nuclear Fusion – Energy Generation in Stars
[1]5.7

If the charge on the condenser of 10°F is doubled, then the energy stored in it becomes

(A) zero

(B) twice that of initial energy

(C) half the initial energy

(D) four times the initial energy

Chapter: [19] Semiconductors
Concept: Energy Bands in Solids
[12]6 | Attempt any six of the following
[2]6.1

Distinguish between the phenomenon of interference and diffraction of light.

Chapter: [11] Interference and Diffraction
Concept: Interference of Light
[2]6.2

Explain how moving coil galvanometer is converted into a voltmeter. Derive the necessary formula.

Chapter: [14] Magnetic Effects of Electric Current
Concept: Moving Coil Galvanometer
[2]6.3

State the advantages of potentiometer over voltmeter.

Chapter: [13] Current Electricity
Concept: Metre Bridge
[2]6.4

Draw a neat, labelled block diagram of a receiver for the detection of amplitude modulated  wave.

Chapter: [20] Communication Systems
Concept: Elements of a Communication System
[2]6.5

A rectangular coil of a moving coil galvanometer contains 100 turns, each having area
15 cm2. It is suspended in the radial magnetic field 0.03 T. The twist constant of suspension
fibre is 15 x 10-10 N-m/degree. Calculate the sensitivity of the moving coil galvanometer.

Chapter: [14] Magnetic Effects of Electric Current
Concept: Moving Coil Galvanometer
[2]6.6

The magnetic flux through a loop is varying according to a relation phi = 6t^2 + 7t + 1 where phi is in milliweber and t is in second. What is the e.m.f. induced in the loop at t = 2 second?

Chapter: [16] Electromagnetic Inductions
Concept: Electromagnetic Induction
[2]6.7

An unknown resistance is placed in the left gap and resistance of 50 ohm is placed in the right gap of a meter bridge. The null point is obtained at 40 cm from the left end. Determine the unknown resistance.

Chapter: [13] Current Electricity
Concept: Meter Bridge
[2]6.8

Find the frequency of revolution of an electron in Bohr’s 2nd orbit; if the radius and speed of electron in that orbit is 2.14 × 10-10 m and 1.09 × 106 m/s respectively. [π= 3.142]

Chapter: [18] Atoms, Molecules and Nuclei
Concept: Bohr'S Model for Hydrogen Atom
[9]7 | Attempt any THREE:
[3]7.1

With the help of neat labelled circuit diagram explain the working of half wave rectifier using semiconductor diode. Draw the input and output waveforms.

Chapter: [19] Semiconductors
Concept: Semiconductor Diode
[3]7.2

Explain self induction and mutual induction

Chapter: [16] Electromagnetic Inductions
Concept: Inductance - Mutual Inductance
[3]7.3

A cube of marble having each side 1 cm is kept in an electric field of intensity 300 V/m. Determine the energy contained in the cube of dielectric constant 8. [Given : ∈0 = 8.85  10–12 C^2/Nm^2]

Chapter: [12] Electrostatics
Concept: Energy of Charged Condenser
[3]7.4

An electron in an atom revolves around the nucleus in an orbit of radius 0.53 Å. If the frequency of revolution of an electron is 9 x109 MHz, calculate the orbital  angular momentum

[Given : Charge on an electron = 1.6 x 10–19 C; Gyromagnetic ratio = 8.8 x 1010 C/kg; π = 3.142]

Chapter: [15] Magnetism
Concept: Magnetic Dipole Moment of a Revolving Electron
[7]8 | Attempt any one of the following
[7]8.1

Describe biprism experiment to calculate the wavelength of a monochormatic light. Draw the necessary ray diagram.

Chapter: [11] Interference and Diffraction
Concept: Measurement of Wavelength by Biprism Experiment

The width of plane incident wavefront is found to be doubled on refraction in denser medium. If it makes an angle of 65° medium. with the normal, calculate the refractive index for the denser medium.

Chapter: [11] Interference and Diffraction
Concept: Measurement of Wavelength by Biprism Experiment
[7]8.2

Draw a neat, labelled energy level diagram for H atom showing the transitions. Explain the series of spectral lines for H atom, whose fixed inner orbit numbers are 3 and 4 respectively.

Chapter: [18] Atoms, Molecules and Nuclei
Concept: Bohr'S Model for Hydrogen Atom

The work functions for potassium and caesium are 2.25 eV and 2.14 eV respectively. Is the photoelectric effect possible for either of them if the incident wavelength is 5180 Å?

[Given : Planck’s constant = 6.63 x 10–34 J.s.;
Velocity of light = 3 x 108 m/s; 1 eV = 1.6 x 10–19 J]

Chapter: [17] Electrons and Photons
Concept: Photoelectric Effect - Hertz’S Observations
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