HSC Science (Electronics) 12th Board ExamMaharashtra State Board
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Question Paper Solutions - Physics 2012 - 2013 HSC Science (Electronics) 12th Board Exam


Marks: 70
[7]1 | Attempt Any One
[7]1.1

Derive an expression for the period of motion of a simple pendulum. On which factors does it depend?

Chapter: [4] Oscillations
Concept: Periodic and Oscillatory Motions

A ballet dancer spins about a vertical axis at 2.5Π rad/s with his both arms outstretched. With the arms folded, the moment of inertia about the same axis of rotation changes by 25%. Calculate the new speed of rotation in r.p.m.

Chapter: [3] Angular Momentum
Concept: Physical Significance of M.I (Moment of Inertia)
[7]1.2

Discuss different modes of vibrations in an air column of a pipe open at both the ends.

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

Draw neat labelled diagrams for modes of vibration of an air column in a pipe when it is closed at one end.

Hence derive an expression for fundamental frequency in each case.

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

A soap bubble of radius 12 cm is blown. Surface tension of soap solution is 30 dyne/cm. Calculate the work done in blowing the soap bubble.

Chapter: [6] Surface Tension
Concept: Capillarity and Capillary Action
[9]2 | Attempt any THREE:
[3]2.1

In a conical pendulum, a string of length 120 cm is fixed at rigid support and carries a mass
of 150 g at its free end. If the mass is revolved in a horizontal circle of radius 0.2 m around a
vertical axis, calculate tension in the string (g = 9.8 m/s2)

Chapter: [6] Surface Tension
Concept: Surface Tension
[3]2.2

Discuss the behaviour of wire under increasing load.

Chapter: [5] Elasticity
Concept: Definition of Stress and Strain
[3]2.3

Derive an expression for one dimensional simple harmonic progressive wave travelling in the
direction of positive X-axis. Express it in ‘two’ different forms.

Chapter: [7] Wave Motion
Concept: Simple Harmonic Progressive Waves,
[3]2.4

The kinetic energy of nitrogen per unit mass at 300 K is 2.5 × 106 J/kg. Find the kinetic energy of 4 kg oxygen at 600 K. (Molecular weight of nitrogen = 28, Molecular weight of oxygen = 32)

Chapter: [4] Oscillations
Concept: K.E.(Kinetic Energy) and P.E.(Potential Energy) in S.H.M.
[12]3 | Attempt any SIX:
[2]3.1

A racing car completes 5 rounds of a circular track in 2 minutes. Find the radius of the track
if the car has uniform centripetal acceleration of Π2 m/s2.

Chapter: [1] Circular Motion
Concept: Dynamics of Uniform Circular Motion - Centripetal Force
[2]3.2

A body weighs 4.0 kg-wt on the surface of the Earth. What will be its weight on the surface of a plant whose mass is `1/8` th of the mass of the Earth and radius half `(1/2)` of that of the Earth?

Chapter: [6] Surface Tension
Concept: Surface Tension
[2]3.3

Define radius of gyration

Chapter: [3] Angular Momentum
Concept: Physical Significance of M.I (Moment of Inertia)

Explain the physical significance of radius of gyration

Chapter: [3] Angular Momentum
Concept: Physical Significance of M.I (Moment of Inertia)
[2]3.4

A body of mass 1 kg is made to oscillate on a spring of force constant 16 N/m. Calculate:

a) Angular frequency

b) frequency of vibration.

Chapter: [4] Oscillations
Concept: Simple Harmonic Motion
[2]3.5

Show that the surface tension of a liquid is numerically equal to the surface energy per unit
area.

Chapter: [6] Surface Tension
Concept: Surface Tension
[2]3.6

Show graphical representation of energy distribution spectrum of perfectly black body.

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Qualitative Ideas of Blackbody Radiation

Explain black body radiation spectrum in terms of wavelength

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Qualitative Ideas of Blackbody Radiation
[2]3.7

‘g’ is the acceleration due to gravity on the surface of the Earth and ‘R’ is the radius of the
Earth.

Show that acceleration due to gravity at height ‘h’ above the surface of the Earth is

`gh = g (R/(R+H))^2`

Chapter: [2] Gravitation
Concept: Acceleration Due to Gravity and Its Variation with Altitude and Depth
[2]3.8

In Melde’s experiment, the number of loops on a string changes from 7 to 5 by the addition of 0.015 kgwt. Find the initial tension applied to the string.

Chapter: [8] Stationary Waves
Concept: Formation of Stationary Waves on String
[7]4 | Select and write the most appropriate answer from the given alternatives for each sub-questions:
[1]4.1

A planet is revolving around a star in a circular orbit of radius R with a period T. If the
gravitational force between the planet and the star is proportional to `R^(-3/2)` then

A) `T^2 prop R^(5/2)`

B) `T^2 prop R^((-7)/2)`

C) `T^2 prop R^(3/2)`

D) `T^2 prop R^4`

Chapter: [1] Circular Motion
Concept: Vertical Circular Motion Due to Earth’s Gravitation
[1]4.2

If ‘L’ is the angular momentum and ‘I’ is the moment of inertia of a rotating body, then `L^2/(2I)`represents its _____

(A) rotational P.E.

(B) total energy

(C) rotational K.E.

(D) translational K.E

Chapter: [3] Angular Momentum
Concept: Definition of M.I., K.E. of Rotating Body
[1]4.3

A particle executing linear S.H.M. has velocities v1 and v2 at distances x1 and x2 respectively from the mean position. The angular velocity of the particle is _______

A) `sqrt((x_1^2 - x_2^2)/(v_2^2 - v_1^2))`

B) `sqrt((v_2^2 - v_1^2)/(x_1^2 - x_2^2))`

C) `sqrt((x_1^2 + x_2^2)/(v_2^2 + v_1^2))`

D) `sqrt((v_2^2 + v_1^2)/(x_2^2 + x_1^2))`

Chapter: [4] Oscillations
Concept: Differential Equation of Linear S.H.M.
[1]4.4

A metal rod having coefficient of linear expansion (α) and Young’s modulus (Y) is heated to
raise the temperature by ΔΘ. The stress exerted by the rod is _______

A) `(Yα)/(ΔΘ)`

B) `(YΔΘ)/α`

C) YαΔΘ

D) `(αΔΘ)/Y`

Chapter: [5] Elasticity
Concept: Definition of Stress and Strain
[1]4.5

A big drop of radius R is formed from 1000 droplets of water. The radius of a droplet will be _______

A) 10 R

B) R/10

C) R/100

D) R/1000

Chapter: [6] Surface Tension
Concept: Surface Tension
[1]4.6

Apparent frequency of the sound heard by a listener is less than the actual frequency of sound emitted by source. In this case _______.

(A) listener moves towards source

(B) source moves towards listener

(C) listener moves away from the source.

(D) source and listener move towards each other.

Chapter: [7] Wave Motion
Concept: Beats

Apparent frequency of the sound heard by a listener is less than the actual frequency of sound emitted by source. In this case _______.

(A) listener moves towards source

(B) source moves towards listener

(C) listener moves away from the source.

(D) source and listener move towards each other.

Chapter: [10] Wave Theory of Light
Concept: Beats
[1]4.7

The substance which allows heat radiations to pass through is _______.

(A) iron

(B) water vapour

(C) wood

(D) dry air

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Temperature and Heat
[7]5 | Attempt Any One
[7]5.1

Obtain an expression for the induced e.m.f. in a coil rotating with uniform angular velocity in
uniform magnetic field. Plot a graph of variation of induced e.m.f. against phase (Θ = ωt) over one cycle.

Chapter: [15] Magnetism
Concept: Magnetic Properties of Materials

The energy density at a point in a medium of dielectric constant 6 is 26.55 × 106 J/m3. Calculate electric field intensity at that point. (ε0 = 8.85 × 10−12 SI units).

Chapter: [12] Electrostatics
Concept: Energy Density of a Medium
[7]5.2

Write notes on Nuclear fission

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

Write notes on Nuclear fusion

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

A galvanometer has a resistance of 16Ω. It shows full scale deflection, when a current of 20 mA is passed through it. The only shunt resistance available is 0.06  which is not appropriate to convert a galvanometer into an ammeter. How much resistance should be connected in series with the coil of galvanometer, so that the range of ammeter is 8 A?

Chapter: [14] Magnetic Effects of Electric Current
Concept: Moving Coil Galvanometer
[9]6 | Attempt any THREE
[3]6.1

Draw a well labelled diagram of photoelectric cell.

Chapter: [17] Electrons and Photons
Concept: Particle Nature of Light

Explain the observations made by Hertz and Lenard about the phenomenon of photoelectric
emission.

Chapter: [17] Electrons and Photons
Concept: Particle Nature of Light
[3]6.2

Explain the working of transistor as a switch.

Chapter: [19] Semiconductors
Concept: Transistor as a Switch
[3]6.3

The refractive indices of water for red and violet colours are 1.325 and 1.334 respectively.
Find the difference between the velocities of rays for these two colours in water. (c = 3 × 108 m/s)

Chapter: [10] Wave Theory of Light
Concept: Polarisation
[3]6.4

In Young’s experiment, the ratio of intensity at the maxima and minima in an interference
pattern is 36 : 9. What will be the ratio of the intensities of two interfering waves?

Chapter: [11] Interference and Diffraction
Concept: Interference of Light Waves and Young’S Experiment
[12]7 | Attempt any SIX:
[2]7.1

Explain the principle of potentiometer.

Chapter: [13] Current Electricity
Concept: Meter Bridge
[2]7.2

Define Magnetic intensity.

Chapter: [15] Magnetism
Concept: Magnetisation and Magnetic Intensity
[2]7.3

What do you mean by polar molecules and non-polar molecules? Give ‘one’ example each.

Chapter: [18] Atoms, Molecules and Nuclei
Concept: Atomic Masses and Composition of Nucleus
[2]7.4

The minimum angular separation between two stars is 4 × 10−6 rad, if telescope is used to observe them with an objective of aperture 16 cm. Find the wavelength of light used.

Chapter: [10] Wave Theory of Light
Concept: Wave Theory of Light
[2]7.5

Explain the need for modulation related to the size of antenna (aerial).

Chapter: [20] Communication Systems
Concept: Modulation and Its Necessity
[2]7.6

Four resistances 4Ω,8Ω,XΩ, and 6Ω are connected in a series so as to form Wheatstone’s
network. If the network is balanced, find the value of ‘X’.

Chapter: [13] Current Electricity
Concept: Wheatstone Bridge
[2]7.7

The magnetic susceptibility of annealed iron at saturation is 4224. Find the permeability of
annealed iron at saturation. (μ0 = 4Π × 10−7 SI unit)

Chapter: [15] Magnetism
Concept: Magnetic Properties of Materials
[7]8 | Select and write the most appropriate answer from the given alternatives for each subquestions:
[1]8.1

A ray of light passes from a vacuum to a medium of refractive index (μ). The angle of
incidence is found to be twice the angle of refraction. The angle of incidence is _______.

A) `cos^(-1)(mu/2)`

B) cos−1(μ)

C)  `2 cos^(-1) (mu/2)`

D) `2 sin^(-1) (mu/2)`

Chapter: [10] Wave Theory of Light
Concept: Polarisation
[1]8.2

The fringes produced in diffraction pattern are of _______.

(A) equal width with same intensity

(B) unequal width with varying intensity

(C) equal intensity\

(D) equal width with varying intensity

Chapter: [11] Interference and Diffraction
Concept: Interference of Light Waves and Young’S Experiment
[1]8.3

If ‘R’ is the radius of dees and ‘B’ be the magnetic field of induction in which positive charges (q) of mass (m) escape from the cyclotron, then its maximum speed (vmax) is _______.

A) `(qR)/(Bm)`

B)`(qm)/(Br)`

C) `(qBR)/m`

D) `m/(qBR)`

Chapter: [16] Electromagnetic Inductions
Concept: Electromagnetic Induction
[1]8.4

The number of photoelectrons emitted _______.

(A) varies inversely with frequency

(B) varies directly with frequency

(C) varies inversely with intensity

(D) varies directly with intensity

Chapter: [17] Electrons and Photons
Concept: Particle Nature of Light
[1]8.5

The width of depletion region of p-n junction diode is _______.

(A) 0.5 nm to 1 nm

(B) 5 nm to 10 nm

(C) 50 nm to 500 nm

(D) 500 nm to 1000 nm

 

Chapter: [19] Semiconductors
Concept: Special Purpose P-n Junction Diodes
[1]8.6

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

(A) amplifier

(B) transducer

(C) receiver

(D) demodulator

Chapter: [20] Communication Systems
Concept: Elements of a Communication System
[1]8.7

A transformer converts 240 V AC to 60 V AC. The secondary has 75 turns. The number of turns in primary are _______.

(A) 600

(B) 500

(C) 400

(D) 300

 

Chapter: [16] Electromagnetic Inductions
Concept: Transformers
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