HSC Science (Electronics) 12th Board ExamMaharashtra State Board
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# Question Paper Solutions - Physics 2014 - 2015 HSC Science (Electronics) 12th Board Exam

SubjectPhysics
Year2014 - 2015 (October)

Marks: 70
[7]1 | Attempt any one of the following :
[7]1.1

State an expression for the moment of intertia of a solid uniform disc, rotating about an axis passing through its centre, perpendicular to its plane. Hence derive an expression for the moment of inertia and radius of gyration:

i. about a tangent in the plane of the disc, and

ii. about a tangent perpendicular to the plane of the disc.

Chapter: [3] Angular Momentum
Concept: Theorems of Perpendicular and Parallel Axes

In a set, 21 turning forks are arranged in a series of decreasing frequencies. Each tuning fork produces 4 beats per second with the preceding fork. If the first fork is an octave of the last fork, find the frequencies of the first and tenth fork.

Chapter: [8] Stationary Waves
Concept: Study of Vibrations of Air Columns
[7]1.2

Discuss the composition of two S.H.M.s along the same path having same period. Find the resultant amplitude and intial phase.

Chapter: [2] Gravitation
Concept: Composition of Two S.H.M.’S Having Same Period and Along Same Line

Discuss the composition of two S.H.M.s along the same path having same period. Find the resultant amplitude and intial phase.

Chapter: [4] Oscillations
Concept: Composition of Two S.H.M.’S Having Same Period and Along Same Line

A sonometer wire is in unison with a tuning fork of frequency 125 Hz when it is stretched by a weight. When the weight is completely immersed in water, 8 beats are heard per second. Find the specific gravity of the material of the weight.

Chapter: [7] Wave Motion
Concept: Formation of Beats
[7]2 | Select and write the most appropriate answer from the given alternatives for each sub-question :
[1]2.1

Which of the following substances is ductile?

(A) Glass

(B) High carbon steel

(C) Steel

(D) Copper

Chapter: [15] Magnetism
Concept: Magnetic Properties of Materials
[1]2.2

Angle of contact for the pair of pure water with clean glass is _______.

(A) acute

(B) obtuse

(C) 90o

(D) 0o

Chapter: [6] Surface Tension
Concept: Surface Tension
[1]2.3

A seconds pendulum is suspended in an elevator moving with constant speed in downward direction. The periodic time (T) of that pendulum is _______.

(A) less than two seconds

(B) equal to two seconds

(C) greater than two seconds

(D) very much greater than two seconds

Chapter: [4] Oscillations
Concept: Periodic and Oscillatory Motions
[1]2.4

The equation of a progressive wave is y = 7 sin (4t - 0.02x), where x and y are in cms and time t in seconds. The maximum velocity of a particle is _______.

(A) 28 cm/s

(B) 32 cm/s

(C) 49 cm/s

(D) 112 cm/s

Chapter: [7] Wave Motion
Concept: Simple Harmonic Progressive Waves,
[1]2.5

The dimensions of emissive power are

(A) [M1 L-2 T-3 ]

(B) [M1 L2 T-3 ]

(C) [M1 L0 T-3 ]

(D) [M1 L0 T-2 ]

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Temperature and Heat
[1]2.6

The pressure (P) of an ideal gas having volume (V) is 2E/3V , then the energy E is _______.

(A) translational kinetic

(B) rotational kinetic

(C) vibrational kinetic

(D) inversely proportional to pressure

Chapter: [4] Oscillations
Concept: Phase of K.E (Kinetic Energy)
[1]2.7

The fundamental frequency of transverse vibration of a stretched string of radius r is proportional to _______.

(A) r-2

(B) r-1

(C) r-1/2

(D) r2

Chapter: [8] Stationary Waves
Concept: Formation of Stationary Waves on String
[12]3 | Attempt any SIX:
[2]3.1

Draw a neat labelled diagram of conical pendulum. State the expression for its periodic time in terms of length.

Chapter: [4] Oscillations
Concept: Periodic and Oscillatory Motions
[2]3.2

A raindrop of diameter 4 mm is about to fall on the ground. Calculate the pressure inside the raindrop. [Surface tension of water T = 0.072 N/m, atmospheric pressure = 1.013 x 105 N/m2 ]

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

Explain why an astronaut in an orbiting satellite has a feeling of weightlessness.

Chapter: [2] Gravitation
Concept: Weightlessness
[2]3.4

The periodic time of a linear harmonic oscillator is 2π second, with maximum displacement of 1 cm. If the particle starts from extreme position, find the displacement of the particle after π/3  seconds.

Chapter: [4] Oscillations
Concept: Periodic and Oscillatory Motions
[2]3.5

State and prove : Law of conservation of angular momentum.

Chapter: [3] Angular Momentum
Concept: Torque and Angular Momentum
[2]3.6

A pinhole is made in a hollow sphere of radius 5 cm whose inner wall is at temperature 727oC. Find the power radiated per unit area. [Stefan’s constant σ = 5.7 x 10-8 J/m2 s K4 , emissivity (e) = 0.2]

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Temperature and Heat
[2]3.7

Draw a neat labelled diagram showing forces acting on the meniscus of water in a capillary tube.

Chapter: [6] Surface Tension
Concept: Surface Tension
[2]3.8

Compute the temperature at which the r.m.s. speed of nitrogen molecules is 832 m/s. [Universal gas constant, R = 8320 J/k mole K, molecular weight of nitrogen = 28.]

Chapter: [9] Kinetic Theory of Gases and Radiation
Concept: Temperature and Heat
[9]4 |  Attempt any THREE :
[3]4.1

Discuss the behaviour of wire under increasing load.

Chapter: [5] Elasticity
Concept: Definition of Stress and Strain
[3]4.2

Determine the binding energy of satellite of mass 1000 kg revolving in a circular orbit around the Earth when it is close to the surface of Earth. Hence find kinetic energy and potential energy of the satellite. [Mass of Earth = 6 x 1024 kg, radius of Earth = 6400 km; gravitational constant G = 6.67 x 10-11 Nm2 /kg2 ]

Chapter: [2] Gravitation
Concept: Binding Energy and Escape Velocity of a Satellite
[3]4.3

Show that all harmonics are present on a stretched string between two rigid supports.

Chapter: [8] Stationary Waves
Concept: Study of Vibrations in a Finite Medium
[3]4.4

A stone of mass 100 g attached to a string of length 50 cm is whirled in a vertical circle by giving velocity at lowest point as 7 m/s. Find the velocity at the highest point. [Acceleration due to gravity = 9.8 m/s2 ]

Chapter: [2] Gravitation
Concept: Acceleration Due to Gravity and Its Variation with Altitude and Depth
[7]5 | Attempt any one of the following :
[7]5.1

Obtain an expression for average power dissipated in a purely resistive A.C. circult. Define power factor of the circuit and state its value for purely resistive A.C. circult.

Chapter: [16] Electromagnetic Inductions
Concept: Power in Ac Circuit: the Power Factor

A rectangular coil of a moving coil galvanometer contains 50 turns each having area 12 cm2 . It is suspended in radial magnetic field 0.025 Wb/m2 by a fibre of twist constant 15 x10-10 Nm/degree. Calculate the sensitivity of the moving coil galvanometer.

Chapter: [14] Magnetic Effects of Electric Current
Concept: Moving Coil Galvanometer
[7]5.2

State Bohr’s third postulate for hydrogen (H2) atom. Derive Bohr’s formula for the wave number. Obtain expressions for longest and shortest wavelength of spectral lines in ultraviolet region for hydrogen atom

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

The photoelectric current in a photoelectric cell can be reduced to zero by a stopping potential of 1.8 volt. Monochromatic light of wavelength 2200Å is incident on the cathode. Find the maximum kinetic energy of the photoelectrons in joules. [Charge on electron = 1.6 x 10-19 C]

Chapter: [17] Electrons and Photons
Concept: Photoelectric Effect - Hertz’S Observations
[7]6 | Select and write the most appropriate answer from the given alternatives for each sub-question :
[1]6.1

Which one of the following particles cannot be accelerated by a cyclotron?

(A) Electrons

(B) Protons

(C) Deuterons

(D) α- particles

Chapter: [14] Magnetic Effects of Electric Current
Concept: Motion in Combined Electric and Magnetic Fields - Cyclotron
[1]6.2

In biprism experiment two interfering waves are produced due to division of _______.

(A) amplitude

(B) wavefront

(C) amplitude and wavefront

(D) neither wavefront nor amplitude

Chapter: [11] Interference and Diffraction
Concept: Measurement of Wavelength by Biprism Experiment
[1]6.3

The output of NOR gate is high, when _______.

(A) all inputs are high

(B) all inputs are low

(C) only one of its inputs is high

(D) only one of its inputs is low

Chapter: [19] Semiconductors
Concept: Digital Electronics and Logic Gates
[1]6.4

Light of a certain wavelength has a wave number barv in vacuum. Its wave number in a medium of refractive index n is _______.

(A)n/barv

(B)1/(nbarv)

(C)barv/n

(D)nbarv

Chapter: [18] Atoms, Molecules and Nuclei
Concept: Wavelength of an Electron
[1]6.5

If the radius of a sphere is doubled without changing the charge on it, then electric flux originating from the sphere is ______.

(A) double

(B) half

(C) same

(D) zero

Chapter: [16] Electromagnetic Inductions
Concept: Inductance - Mutual Inductance
[1]6.6

The momentum of a photon of de Broglie wavelength 5000Å is _______.

[Planck’s constant = 6.63 x10-34 J.s.]

(A) 1.326 x10-28 kg-m/s

(B) 7.54 x10-28 kg-m/s

(C) 1.326 x10-27 kg-m/s

(D) 7.54 x10-27 kg-m/s

Chapter: [17] Electrons and Photons
Concept: Einstein’s Equation - Particle Nature of Light
[1]6.7

Ionosphere mainly consists of _______.

(A) positive ions and electrons

(B) water vapour and smoke

(C) ozone layer

(D) dust particles

Chapter: [17] Electrons and Photons
Concept: Photoelectric Effect - Hertz’S Observations
[12]7 | Attempt any SIX:
[2]7.1

State any ‘two’ possible sources of errors in meter-bridge experiment. How can they be minimised?

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

A potentionmeter wire has resistance of per unit length of 0.1 Ω/m. A cell of e.m.f. 1.5V balances against 300 cm length of the wire. Find the current in the potentiometer wire.

Chapter: [13] Current Electricity
Concept: Potentiometer
[2]7.3

Give any ‘two’ points of differences between diamagnetic and ferromagnetic substances.

Chapter: [15] Magnetism
Concept: Magnetic Properties of Materials
[2]7.4

An iron rod of area of cross-section 0.1m2 is subjected to a magnetising 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]

Chapter: [15] Magnetism
Concept: Magnetic Properties of Materials
[2]7.5

Draw a neat labelled circuit diagram of experimental arrangement for study of photoelectric effect.

Chapter: [17] Electrons and Photons
Concept: Photoelectric Effect - Hertz’S Observations
[2]7.6

A coil of 100 turns, each of area 0.02m2 is kept in a uniform field of induction 3.5 x10-5 T. If the coil rotates with a speed of 6000 r.p.m. about an axis in the plane of the coil and perpendicular to the magnetic induction, calculate peak value of e.m.f. induced in the coil.

Chapter: [16] Electromagnetic Inductions
Concept: Coil Rotating in Uniform Magnetic Induction
[2]7.7

Define modulation and transducer

Chapter: [20] Communication Systems
Concept: Modulation and Its Necessity
[2]7.8

In a biprism experiment, when a convex lens was placed between the biprism and eyepiece at a distance of 30 cm from the slit, the virtual images of the slits are found to be separated by 7 mm. If the distance between the slit and biprism is 10 cm and between the biprism and eyepiece is 80cm, find the linear magnification of the image.

Chapter: [11] Interference and Diffraction
Concept: Measurement of Wavelength by Biprism Experiment
[9]8 | Attempt any THREE:
[3]8.1

With the help of a neat circuit diagram, explain the working of a photodiode.

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

State its any ‘two’ uses of photodiode.

Chapter: [19] Semiconductors
Concept: Special Purpose P-n Junction Diodes
[3]8.2

A parallel beam of monochromatic light is incident on a glass slab at an angle of incidence 60o. Find the ratio of width of the beam in the glass to that in the air if refractive index of glass is 3/2.

Chapter: [11] Interference and Diffraction
Concept: Interference of Light
[3]8.3

With the help of neat diagram, explain how non-polar dielectric material is polarised in external electric field of increasing intensity. Define polarisation in dielectrics.

Chapter: [10] Wave Theory of Light
Concept: Polarisation
[3]8.4

In a single slit diffraction pattern, the distance between first minima on the right and first minima on the left of central maximum is 4 mm. The screen on which the pattern is displaced, is 2m from the slit and wavelength of light used is 6000Å. Calculate width of the slit and width of the central maximum.

Chapter: [11] Interference and Diffraction
Concept: Fraunhofer Diffraction Due to a Single Slit
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