# Physics 2013-2014 HSC Science (Electronics) 12th Standard Board Exam Question Paper Solution

Physics
Date: March 2014

 1 | Attempt any SIX
 1.1

Explain the rise of liquid in the capillary on the basis of pressure difference.

Concept: Capillarity and Capillary Action
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
 1.2

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

Concept: Qualitative Ideas of Black Body Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 1.3

The escape velocity of a body from the surface of the earth is 11.2 km/s. If a satellite were to orbit close to the surface, what would be its critical velocity?

Concept: Binding Energy and Escape Velocity of a Satellite
Chapter: [0.02] Gravitation
 1.4

A pipe which is open at both ends is 47 cm long and has an inner diameter 5 cm. If the speed of sound in air is 348 m/s, calculate the fundamental frequency of air column in that pipe.

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
 1.5

Show that R.M.S. velocity of gas molecules is directly proportional to square root of its absolute temperature.

Concept: Assumptions of Kinetic Theory of Gases
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 1.6

For a particle performing uniform circular motion vecv=vecomegaxxvecrobtain an expression for linear acceleration of the particle performing non-uniform circular motion.

Concept: Uniform Circular Motion (UCM)
Chapter: [0.01] Circular Motion
 1.7

A stone of mass 1 kg is whirled in horizontal circle attached at the end of a 1 m long string. If the string makes an angle of 30º with vertical, calculate the centripetal force acting on the stone.(g=9.8m/s2).

Concept: Centrifugal Forces
Chapter: [0.01] Circular Motion
 1.8

A solid cylinder of uniform density of radius 2 cm has mass of 50 g. If its length is 12 cm, calculate its moment of inertia about an axis passing through its centre and perpendicular to its length.

Concept: Physical Significance of M.I (Moment of Inertia)
Chapter: [0.03] Angular Momentum
 2 | Attempt any THREE:
 2.1

Derive an expression for acceleration due to gravity at depth ‘d’ below the earth’s surface.

Concept: Acceleration Due to Gravity and Its Variation with Altitude and Depth
Chapter: [0.02] Gravitation
 2.2

A copper metal cube has each side of length 1 m. The bottom edge of the cube is fixed and tangential force 4.2x108 N is applied to a top surface. Calculate the lateral displacement of the top surface if modulus of rigidity of copper is 14x1010 N/m2.

Concept: Periodic and Oscillatory Motion
Chapter: [0.04] Oscillations [0.05] Oscillations
 2.3

State an expression for K. E. (kinetic energy) and P. E. (potential energy) at displacement ‘x’ for a particle performing linear S.H. M. Represent them graphically. Find the displacement at which K. E. is equal to P. E.

Concept: K.E.(Kinetic Energy) and P.E.(Potential Energy) in S.H.M.
Chapter: [0.04] Oscillations
 2.4

The equation of simple harmonic progressive wave is given by y=0.05sinpi[20t-x/6] where all quantities are in S. I. units. Calculate the displacement of a particle at 5 m from origin and at the instant 0.1 second.

Concept: Simple Harmonic Progressive Waves,
Chapter: [0.07] Wave Motion
 3 | Attempt Any One
 3.1
 3.1.1

State the theorem of parallel axes about moment of inertia.

Concept: Physical Significance of M.I (Moment of Inertia)
Chapter: [0.03] Angular Momentum

Prove the theorem of parallel axes about moment of inertia

Concept: Theorems of Perpendicular and Parallel Axes
Chapter: [0.01] Rotational Dynamics [0.03] Angular Momentum
 3.1.2

Calculate the density of paraffin oil, if glass capillary of diameter 0.25 mm dipped in paraffin oil of surface tension 0.0245 N/m rises to a height of 4 cm. (Angle of contact of paraffin with glass = 28° and acceleration due to gravity = 9.8 m/s2.)

Concept: Capillarity and Capillary Action
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
 3.2
 3.2.1

A wire of density ‘ρ’ and Young’s modulus ‘Y’ is stretched between two rigid supports separated by a distance ‘L’ under tension ‘T’. Derive an expression for its frequency in fundamental mode. Hence show that n=1/(2L)sqrt((Yl)/(rhoL)) where symbols have their usual meanings

Concept: Reflection of Transverse and Longitudinal Waves
Chapter: [0.07] Wave Motion
 3.2.2

When the length of a simple pendulum is decreased by 20 cm, the period changes by 10%. Find the original length of the pendulum.

Concept: Some Systems Executing Simple Harmonic Motion
Chapter: [0.04] Oscillations
 4 | Select and write the most appropriate answer from the given alternatives for each sub-question
 4.1

The bulging of earth at the equator and flattening at the poles is due to _______.

Centripetal Force

Centrifugal Force

Gravitational Force

Electrostatic Force

Concept: Centrifugal Forces
Chapter: [0.01] Circular Motion
 4.2

Young’s modulus of material of wire is ‘Y’ and strain energy per unit volume is ‘E’, then the strain is

(A) sqrtY/(2E)

(B) sqrt(E/Y)

(C) sqrt((2E)/Y)

(D) sqrt(2EY)

Concept: Hooke’s Law
Chapter: [0.05] Elasticity
 4.3

The wavelength range of thermal radiation is

(A) from 4000 Å to 7000 Å

(B) from 7700 Å to 4 x 106 Å

(C) from 106 Å to 108 Å

(D) from 4 x 10-12 Å to 4 x 108 Å

Concept: Qualitative Ideas of Black Body Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 4.4

A pipe open at both ends resonates to a frequency ‘n1’ and a pipe closed at one end resonates to a frequency ‘n2’. If they are joined to form a pipe closed at one end, then the fundamental frequency will be ______.

(A)  (n_1n_2)/(2n_2+n_1)

(B) (2n_2n_1)/(2n_2+n_1)

(C) (2n_2n_1)/(n_1+n_2)

(D) (n_2+2n_1)/(n_1n_2)

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
 4.5

The phase difference between displacement and acceleration of a particle performing S.H.M. is _______.

(A) pi/2rad

(D)(3pi)/2rad

Concept: Some Systems Executing Simple Harmonic Motion
Chapter: [0.04] Oscillations
 4.6

Let n1 and n2 be the two slightly different frequencies of two sound waves. The time interval between waxing and immediate next waning is ______.

(A) 1/(n_1-n_2)

(B) 2/(n_1-n_2)

(C) (n_1-n_2)/2

(D) 1/(2(n_1-n_2))

Concept: Formation of Beats
Chapter: [0.07] Wave Motion
 4.7

A metal ball cools from 64 °C to 50 °C in 10 minutes and to 42 °C in next 10 minutes. The ratio of rates of fall of temperature during the two intervals is _______.

4/7

7/4

2

2.5

Concept: Heat and Temperature
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 5 | Attempt any SIX
 5.1

Show that the orbital magnetic dipole moment of a revolving electron is (eVr)/2

Concept: Magnetic Dipole Moment of a Revolving Electron
Chapter: [0.15] Magnetism
 5.2

Describe the construction of photoelectric cell.

Concept: Wave Nature of Matter
Chapter: [0.18] Atoms, Molecules and Nuclei
 5.3

For a glass plate as a polariser with refractive index 1.633, calculate the angle of incidence at which light is polarised.

Concept: Polarisation
Chapter: [0.1] Wave Theory of Light
 5.4

The susceptibility of magnesium at 300 K is 2.4 x 10-5. At what temperature will the susceptibility increase to 3.6 x 10-5?

Concept: Heat and Temperature
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 5.5

Draw a neat labelled diagram for Davisson and Germer experiment, for diffraction of electron wave.

Concept: Davisson and Germer Experiment
Chapter: [0.18] Atoms, Molecules and Nuclei
 5.6

Write the functions of the following in communication systems:

Transmitter

Concept: Basic Terminology Used in Electronic Communication Systems
Chapter: [0.2] Communication Systems

Write the functions of the following in communication systems:

Concept: Basic Terminology Used in Electronic Communication Systems
Chapter: [0.2] Communication Systems
 5.7

A metal rod 1/sqrtpi m long rotates about one of its ends perpendicular to a plane whose magnetic induction is 4 x 10-3 T. Calculate the number of revolutions made by the rod per second if the e.m.f. induced between the ends of the rod is 16 mV.

Concept: Electromagnetic Induction
Chapter: [0.12] Electromagnetic Induction [0.16] Electromagnetic Inductions
 5.8

Find the wave number of a photon having energy of 2.072 eV

Given : Charge on electron = 1.6 x 10-19 C,

Velocity of light in air = 3 x 108 m/s,

Planck’s constant = 6.63 x 10-34 J-s.

Concept: Einstein’s Equation - Particle Nature of Light
Chapter: [0.17] Electrons and Photons
 6 | Attempt any THREE
 6.1

State Ampere’s circuital law.

Concept: Ampere’s Circuital Law
Chapter: [0.14] Magnetic Effects of Electric Current

Obtain an expression for magnetic induction along the axis of the toroid.

Concept: Ampere’s Circuital Law
Chapter: [0.14] Magnetic Effects of Electric Current
 6.2

Calculate the radius of second Bohr orbit in hydrogen atom from the given data.

Mass of electron = 9.1 x 10-31kg

Charge on the electron = 1.6 x 10-19 C

Planck’s constant = 6.63 x 10-34 J-s.

Permittivity of free space = 8.85 x 10-12 C2/Nm2

Concept: Bohr’s Model for Hydrogen Atom
Chapter: [0.18] Atoms, Molecules and Nuclei
 6.3

Explain the working of P-N junction diode in forward and reverse biased mode.

Concept: Semiconductor Diode
Chapter: [0.19] Semiconductors
 6.4

A network of four capacitors of 6 μF each is connected to a 240 V supply. Determine the charge on each capacitor. Concept: Condensers in Series and Parallel,
Chapter: [0.12] Electrostatics
 7 | Attempt Any One
 7.1
 7.1.1

Describe biprism experiment to find the wavelength of monochromatic light. Draw the necessary ray diagram for magnified and diminished images of virtual sources.

Concept: Measurement of Wavelength by Biprism Experiment
Chapter: [0.11] Interference and Diffraction
 7.1.2

If the difference in velocities of light in glass and water is 2.7 x 107 m/s, find the velocity of light in air. (Refractive index of glass = 1.5, Refractive index of water = 1.333)

Concept: Equation for Velocity and Energy at Different Positions of Vertical Circular Motion
Chapter: [0.01] Circular Motion
 7.2
 7.2.1

Explain transformer working with construction.

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

State the principle on  which transformer works.

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

Derive an expression for ratio of e.m.f.s and currents in terms of number of turns in primary and secondary coil.

Concept: Transformers
Chapter: [0.12] Electromagnetic Induction [0.16] Electromagnetic Inductions
 7.2.2

Two diametrically opposite points of a metal ring are connected to two terminals of the left gap of meter bridge. The resistance of 11 Ω is connected in right gap. If null point is obtained at a distance of 45 cm from the left end, find the resistance of metal ring.

Concept: Meter Bridge
Chapter: [0.13] Current Electricity
 8 | Select and write the most appropriate answer from the given alternatives for each sub-question
 8.1

Intensity of electric field at a point close to and outside a charged conducting cylinder is proportional to ______. (r is the distance of a point from the axis of cylinder)

(A) 1/r

(B) 1/r^2

(C) 1/r^3

(D) r3

Concept: Energy of Charged Condenser
Chapter: [0.12] Electrostatics
 8.2

When a hole is produced in P-type semiconductor, there is _______.

extra electron in valence band.

extra electron in conduction band.

missing electron in valence band.

missing electron in conduction band.

Concept: Electrical Properties - Applications of n-type and p-type Semiconductors
Chapter: [0.19] Semiconductors
 8.3

The outermost layer of the earth’s atmosphere is _______.

(A) stratosphere

(B) mesospher

(C) troposphere

(D) ionosphere

Concept: Propagation of Electromagnetic Waves
Chapter: [0.2] Communication Systems
 8.4

Accuracy of potentiometer can be easily increased by ______

(A) increasing resistance of wire

(B) decreasing resistance of wire

(C) increasing the length of wire

(D) decreasing the length of wire

Concept: Metre Bridge
Chapter: [0.13] Current Electricity
 8.5

When electron in hydrogen atom jumps from second orbit to first orbit, the wavelength of radiation emitted is λ. When electron jumps from third orbit to first orbit, the wavelength of emitted radiation would be _______.

(A)27/32lambda

(B)32/27lambda

(C)2/3lambda

(D)3/2lambda

Concept: Qualitative Ideas of Black Body Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 8.6

An ideal voltmeter has _______.

(A) low resistance

(b) high resistance

(C) infinite resistance

(D) zero resistance

Concept: Moving Coil Galvanometer
Chapter: [0.09] Current Electricity [0.14] Magnetic Effects of Electric Current
 8.7

The resolving power of telescope of aperture 100 cm for light of wavelength 5.5 x 10-7 m is _______________.

0.149 x 107

1.49 x 107

14.9 x 107

149 x 107

Concept: Resolving Power of a Microscope and Telescope
Chapter: [0.11] Interference and Diffraction

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