# Physics 2012-2013 HSC Science (Electronics) 12th Board Exam Question Paper Solution

Physics
Date: March 2013

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

The moment of inertia of a thin uniform rod of mass M and length L, about an axis passing through a point, midway between the centre and one end, perpendicular to its length is .....

(a)48/7ML^2

(b)7/48ML^2

(c)1/48ML^2

(d)1/16ML^2

Concept: Physical Significance of M.I (Moment of Inertia)
Chapter: [0.03] Angular Momentum
[1]1.2

'n' droplets of equal size of radius r coalesce to form a bigger drop of radius R. The energy liberated is equal to...................

(T =Surface tension of water)

(a) 4piR^2T[n^(1/3)-1]

(b) 4pir^2T[n^(1/3)-1]

(c) 4piR^2T[n^(2/3)-1]

(d)4 pir^2T[n^(2/3)-1]

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[1]1.3

The buckling of a beam is found to be more if ___ .

(a) the breadth of the beam is large.

(b) the beam material has large value of Young's -modulus.

(c) the length of the beam is small.

(d) the depth of the beam is small.·

Concept: Hooke’s Law
Chapter: [0.05] Elasticity
[1]1.4

When a transverse wave on a string is reflected from the free end, the phase change produced is ..............

(b)  pi/2  rad

(c) (3pi)/4 rad

(d) pi  rad

Concept: Reflection of Transverse and Longitudinal Waves
Chapter: [0.07] Wave Motion
[1]1.5

The number of degrees of freedom for a rigid diatomic molecule is.................

(a) 3

(b) 5

(c) 6

(d) 7

Concept: Projection of U.C.M.(Uniform Circular Motion) on Any Diameter
Chapter: [0.04] Oscillations
[1]1.6

Two particles perform linear simple harmonic motion along the same path of length 2A and period T as shown in the graph below. The phase difference between them is ___________.

pi/4 rad

pi/2 rad

(3pi)/4 rad

Concept: Differential Equation of Linear S.H.M.
Chapter: [0.04] Oscillations [0.05] Oscillations
[1]1.7

The light from the Sun is found to have a maximum intensity near the wavelength of 470 nm. Assuming the surface of the Sun as a black body, the temperature of the Sun is _____________.

[Wien's constant b = 2 .898 x l0- 3mK]

5800 K

6050 K

6166 K

6500 K

Concept: Temperature and Heat
Chapter: [0.09] Kinetic Theory of Gases and Radiation
[12]2 | Attempt any SIX :
[2]2.1

State Kepler's law of orbit and law of equal areas.

Concept: Kepler’S Laws
Chapter: [0.02] Gravitation
[2]2.2

A car of mass 1500Kg rounds a curve of radius 250m at 90 Km/hour. Calculate the centripetal force acting on it.

Concept: Dynamics of Uniform Circular Motion - Centripetal Force
Chapter: [0.01] Circular Motion
[2]2.3

Draw a neat labelled diagram for Ferry's perfectly black body.

Concept: Qualitative Ideas of Blackbody Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
[2]2.4

A mass M attached to a spring oscillates with a period of 2 seconds. If the mass is increased by 2 Kg, the eriod increases by 1 second. Find the initial mass, assuming that Hooke's law is obeyed.

Concept: Hooke’s Law
Chapter: [0.05] Elasticity
[2]2.5

Differentiate between free and forced vibrations .

Concept: Free and Forced Vibrations
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
[2]2.6

The surface tension of water at 0ºc is 75·5 dyne/cm. Find surface tension of water at 25°C. [ α for water = 0·0021/°C ]

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[2]2.7

Derive the relation between surface tension and surface energy per unit area.

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
[2]2.8

A wheel of moment of inertia 1 Kgm 2 is rotating at a speed of 40 rad/s. Due to friction on the axis, the wheel comes to rest in 10 minutes. Calculate the angular momentum of the wheel, two minutes before it comes to rest.

Concept: Physical Significance of M.I (Moment of Inertia)
Chapter: [0.03] Angular Momentum
[9]3 | Attempt any THREE :
[3]3.1

A particle of mass m, just completes the vertical circular motion. Derive the expression for the difference in tensions at the highest and the lowest points.

Concept: Dynamics of Uniform Circular Motion - Centripetal Force
Chapter: [0.01] Circular Motion
[3]3.2

The Earth is rotating with angular velocity ω about its own axis. R is the radius of the Earth. If Rω2 = 0 · 03386 m/ s2 , calculate the weight of a body of mass 100 gram at latitude 25°.   (g=9·8m/s2).

Concept: Angular Velocity
Chapter: [0.01] Circular Motion
[3]3.3

Derive an expression for kinetic energy, when a rigid body is rolling on a horizontal surface without slipping. Hence find kinetic energy for a solid sphere.

Concept: Rolling Motion
Chapter: [0.01] Rotational Dynamics [0.03] Angular Momentum
[3]3.4

A steel wire-of diameter 1 x 10-3m is stretched by a force of 20 N. Calculate the strain energy per unit volume.(Y steel= 2 x 1011 N /m2)

Concept: Definition of Stress and Strain
Chapter: [0.05] Elasticity
[7]4 | Attempt any one of the following :
[7]4.1

Define an ideal simple pendulum.

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

Show that, under certain conditions, simple pendulum performs the linear simple harmonic motion.

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

A train blows a whistle of frequency 640 Hz in air. Find the difference in apparent frequencies of the whistle for a stationary observer, when the train moves towards and away from the observer with the speed of 72 Km/hour. [Speed of sound in air = 340 m/s.]

Concept: Formation of Beats
Chapter: [0.07] Wave Motion
[7]4.2

With a neat labelled diagram, show that all harmonics are present in an air column contained in a pipe open at both the ends. Define end correction.

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

Calculate the kinetic energy of 10 gram of Argon molecules at 127°C.
[Universal gas constant R = 8320 J/k mole K. Atomic weight of Argon = 40]

Concept: Phase of K.E (Kinetic Energy)
Chapter: [0.04] Oscillations
[7]5 | Select and write the most appropriate answer from the given alternatives for each sub-question :
[1]5.1

In the diffraction pattern due to a single slit of width 'd' with incident light of wavelength 'λ', at an angle of  diffraction θ. the condition for first minimum is ....

(a)lambda sin theta =d

(b) d costheta =lambda

(c)d sintheta=lambda

(d) lambda cos theta=d

Concept: Fraunhofer Diffraction Due to a Single Slit
Chapter: [0.11] Interference and Diffraction
[1]5.2

Kirchhoff's junction law is equivalent to .............................
(a) conservation of energy.
(b) conservation of charge
(c) conservation of electric potential
(d) conservation of electric flux

Concept: Kirchhoff’s Rules
Chapter: [0.13] Current Electricity
[1]5.3

Let 'p'  and 'E' denote the linear momentum and energy of emitted photon respectively. If the wavelength of incident radiation is increased ___ .
(a) both p and E increase
(b) p increases and E decreases
(c) p decreases and E increases
(d) both p and E decrease.

Concept: Qualitative Ideas of Blackbody Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
[1]5.4

The nuclei having same number of protons but different number of neutrons are called ___ .
(a) isobars

(b) a-particles

(c) isotopes

(d) y-particles

Concept: Hydrogen Spectrum
Chapter: [0.18] Atoms, Molecules and Nuclei
[1]5.5

In case of transistor oscillator, to obtain sustained oscillations, the product of voltage gain without feedback and feedback factor should be __________.

zero

less than 1

one

infinity

Concept: Oscillators
Chapter: [0.19] Semiconductors
[1]5.6

The process of regaining of information from carrier wave at the receiver is called .................

(a) modulation

(b) transmission

(c) propagation

(d) demodulation

Concept: Need for Modulation and Demodulation
Chapter: [0.2] Communication Systems
[1]5.7

Reactance of a coil is 157 Ω. On connecting the coil across a source of frequency 100 Hz, the current lags behind e.m.f. by 45°. The inductance of the coil is ...........

(a) 0·25 H

(b) 0·5 H

(c) 4 H

(d) 314H

Concept: Reactance and Impedance
Chapter: [0.16] Electromagnetic Inductions
[12]6 | Attempt any SIX :
[2]6.1

Draw a neat labelled diagram of a parallel plate capacitor completely filled with dielectric.

Concept: The Parallel Plate Capacitor
Chapter: [0.12] Electrostatics
[2]6.2

A point is situated at 7cm and 7·2 cm from two coherent sources. Find the· nature of illumination at the point if wavelength of light is 4000A.

Concept: Fraunhofer Diffraction Due to a Single Slit
Chapter: [0.11] Interference and Diffraction
[2]6.3

Obtain the expression for current sensitivity of moving coil galvanometer.

Concept: Moving Coil Galvanometer
Chapter: [0.14] Magnetic Effects of Electric Current
[2]6.4

In a cyclotron, magnetic field of 3·5Wb/m2 is used to accelerate protons. What should be the time interval in which the electric field between the Dees be reversed?
(Mass of proton = 1· 67 x 10-27Kg, Charge on proton =1·6x10-19c).

Concept: Motion in Combined Electric and Magnetic Fields - Cyclotron
Chapter: [0.14] Magnetic Effects of Electric Current
[2]6.5

Define magnetization. State its formula and S.I. unit.

Concept: Magnetisation and Magnetic Intensity
Chapter: [0.15] Magnetism
[2]6.6

Electrostatic energy of 3·5 x 10-4 J is stored in a capacitor at 700 V. What is the charge on the capacitor?

Concept: Energy of Charged Condenser
Chapter: [0.12] Electrostatics
[2]6.7

What is space wave propagation?

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

State three components of space wave propagation.

Concept: Propagation of Electromagnetic Waves
Chapter: [0.2] Communication Systems
[2]6.8

Find the value of energy of electron in eV in the third Bohr orbit of hydrogen atom.

(Rydberg's constant (R) = 1· 097 x 107m - 1,Planck's constant (h) =6·63x10-34 J-s,Velocity of light in air (c) = 3 x 108m/ s.)

Concept: Einstein’s Equation - Particle Nature of Light
Chapter: [0.17] Electrons and Photons
[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.

Concept: Semiconductor Diode
Chapter: [0.19] Semiconductors
[3]7.2

A cell balances against a length of 200 cm on a potentiometer wire, when it is shunted by a resistance of 8Ω. The balancing length reduces by 40 cm, when it is shunted by a resistance of 4 Ω . Calculate the balancing length when the cell is in open circuit. Also calculate the internal resistance of the cell.

Concept: Metre Bridge
Chapter: [0.13] Current Electricity
[3]7.3

State the law of radioactive decay.

Chapter: [0.15] Structure of Atoms and Nuclei [0.18] Atoms, Molecules and Nuclei

Derive the mathematical expression for law of radioactive decay for a sample of a radioactive nucleus

Chapter: [0.15] Structure of Atoms and Nuclei [0.18] Atoms, Molecules and Nuclei
[3]7.4

The photoelectric work function for a metal is 4.2 eV. If  the stopping potential is 3V, find the threshold wavelength and maximum kinetic energy of emitted electrons.

(Velocity of light in air = 3 x 108m/s,
Planck's constant = 6·63 x10-34 J -s,
Charg.e ori electron = 1·6 x 10 -19 C)

Concept: Photoelectric Effect - Hertz’S Observations
Chapter: [0.17] Electrons and Photons
[7]8 | Attempt any one :
[7]8.1

State Faraday's laws of electromagnetic induction.

Chapter: [0.16] Electromagnetic Inductions

State Lenz's Law.

Concept: Lenz’S Law and Conservation of Energy
Chapter: [0.16] Electromagnetic Inductions

A circular coil of 250 turns and diameter 18 cm carries a current of 12A. What is the magnitude of magnetic moment associated with the coil?

Concept: Moving Coil Galvanometer
Chapter: [0.14] Magnetic Effects of Electric Current
[7]8.2

On the basis of Huygens' wave theory of light prove that velocity of light in a rarer medium is greater than velocity of light in a denser medium.

Concept: Huygens Principle
Chapter: [0.1] Wave Theory of Light

In Young' s experiment the ratio of intensity at the maxima and minima . in the interference pattern is 36 : 16. What is the ratio of the widths of the two slits?

Concept: Interference of Light Waves and Young’S Experiment
Chapter: [0.11] Interference and Diffraction

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