# Physics 2017-2018 HSC Science (Computer Science) 12th Board Exam Question Paper Solution

Physics
Date & Time: 26th February 2018, 11:00 am
Duration: 3h

1 | Select and write the most appropriate answer from the given alternative for each sub-question
1.1

In the stationary wave, the distance between a node and its adjacent antinode is _______.

(a) λ

(b) lambda/4

(c) lambda/2

(d)  2λ

Concept: Formation of Stationary Waves on String
Chapter: [0.08] Stationary Waves
1.2

If the source is moving away from the observer, then the apparent frequency _____.

(a) will increase

(b) will remain the same

(c) will be zero

(d) will decrease

Concept: Wave Motion Introduction
Chapter: [0.07] Wave Motion
1.3

A particle of mass m performs the vertical motion in a circle of radius r. Its potential energy at the highest point is _______. (g is acceleration due to gravity)

2 mgr

mgr

0

3 mgr

Concept: Vertical Circular Motion Due to Earth’s Gravitation
Chapter: [0.01] Circular Motion
1.4

The compressibility of a substance is the reciprocal of _________.

(a) Young’s modulus

(b) bulk modulus

(c) modulus of rigidity

(d) Poisson's ratio

Concept: Eneral Explanation of Elastic Property
Chapter: [0.05] Elasticity
1.5

If the particle starts its motion from mean position, the phase difference between displacement and acceleration is ______.

pi/2 rad

pi  rad

pi/4 rad

Concept: Some Systems Executing Simple Harmonic Motion
Chapter: [0.04] Oscillations
1.6

The kinetic energy per molecule of a gs at temperature T is ________.

(a) (3/2)RT

(b) (3/2)K_BT

(c) (2/3) RT

(d) (3/2)("RT"/M)

Concept: Temperature and Heat
Chapter: [0.09] Kinetic Theory of Gases and Radiation
1.7

A thin ring has mass 0.25 kg and radius 0.5 m. Its moment of inertia about an axis passing through its centre and perpendicular to its plane is _______.

0. 0625 kg m2

0.625 kg m2

6. 25 kg m2

62. 5 kg m2

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

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

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

State any four assumptions of kinetic theory of gases.

Concept: Kinetic Theory of Gases- Assumptions
Chapter: [0.09] Kinetic Theory of Gases and Radiation
2.3

Define moment of inertia. State its SI unit and dimensions.

Concept: Physical Significance of M.I (Moment of Inertia)
Chapter: [0.03] Angular Momentum
2.4

Distinguish between centripetal and centrifugal force.

Concept: Centrifugal Forces
Chapter: [0.01] Circular Motion
2.5

In Melde’s experiment, when the tension in the string is 10 g wt then three loops are obtained. Determine the tension in the string required to obtain four loops, if all other conditions are constant.

Concept: Formation of Stationary Waves on String
Chapter: [0.08] Stationary Waves
2.6

Calculate the work done in increasing the radius of a soap bubble in air from 1 cm to 2 cm. The surface tension of soap solution is 30 dyne/cm. (Π = 3.142).

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

A falt curve on a highways has a radius of curvature 400 m. A car goes around a curve at a speed of 32 m/s. What is the minimum value of the coefficient of friction that will prevent the car from sliding? (g = 9.8 m/ s2)

Chapter: [0.01] Circular Motion
2.8

A particle performing linear S.H.M. has the maximum velocity of 25 cm/s and maximum acceleration of 100 cm/ m2. Find the amplitude and period of oscillation. (π = 3.142)

Concept: Differential Equation of Linear S.H.M.
Chapter: [0.04] Oscillations [0.05] Oscillations
3 | Attempt Any Three
3.1

Derive Laplace’s law for spherical membrane of bubble due to surface tension.

Concept: Surface Tension
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
3.2

State and prove : Law of conservation of angular momentum.

Concept: Torque and Angular Momentum
Chapter: [0.01] Rotational Dynamics [0.03] Angular Momentum
3.3

Calculate the strain energy per unit volume is a brass wire of length 3 m and area of cross - section 0.6 mm2 when it is stretched by 3 mm and a force of 6 kgwt is applied to its free end.

Concept: Definition of Stress and Strain
Chapter: [0.05] Elasticity
3.4

What is the decrease in weight of a body of mass 500 kg when it is taken into a mine of depth 1000 km? (Radius of earth R = 6400 km, g = 9.8 m/s2)

Concept: Acceleration Due to Gravity and Its Variation with Altitude and Depth
Chapter: [0.02] Gravitation
4 | Attempt Any One
4.1

State the differential equation of linear simple harmonic motion.

Concept: Simple Harmonic Motion
Chapter: [0.04] Oscillations

Hence obtain the expression for acceleration, velocity and displacement of a particle performing linear S.H.M.

Concept: Simple Harmonic Motion
Chapter: [0.04] Oscillations

A body cools from 80° C to 70° C in 5 minutes and to 62° C in the next 5 minutes. Calculate the temperature of the surroundings.

Concept: Temperature and Heat
Chapter: [0.09] Kinetic Theory of Gases and Radiation
4.2

What is meant by harmonics?

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

Show that only odd harmonics are present as overtones in the case of an air column vibrating in a pipe closed at one end.

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

The wavelengths of two sound waves in air are 81/173m and 81/170m. They produce 10 beats per second. Calculate the velocity of sound in air

Concept: Wave Motion
Chapter:
5 | Select and write the most appropriate answer from the given alternatives for each sub-question :
5.1

The reflected waves from an ionosphere are _____.

(a) ground waves

(b) sky waves

(c) space waves

(d) very high-frequency waves

Concept: Propagation of Electromagnetic Waves
Chapter: [0.2] Communication Systems
5.2

In interference pattern, using two coherent sources of light; the fringe width is ________

(a) directly proportional to the wavelength

(b) inversely proportional to the square of the wavelength

(c) inversely proportional to wavelength.

(d) directly proportional to the square of the wavelength.

Concept: Interference of Light
Chapter: [0.11] Interference and Diffraction
5.3

Electric intensity outside a charged cylinder having the charge per unit length 'λ' at a distance from its axis is ________.

(a) E = (2pi in_0 lambda)/(Kr^2)

(b) E = (in_0 lambda)/(2piKr^2)

(c) E = lambda/(2piin_0Kr)

(d) E = (4piin_0lambda)/(Kr^2)

Concept: Applications of Gauss’s Law
Chapter: [0.12] Electrostatics
5.4

SI unit of potential gradient is _______.

(a) V cm

(b) V/"cm"

(c) Vm

(d) V/m

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
5.5

The momentum associated with the photon is given by_______.

(a) hv

(b) "hv"/c

(c) hE

(d) hλ

Concept: Particle Nature of Light
Chapter: [0.17] Electrons and Photons
5.6

A pure semiconductor is ________.

(a) an extrinsic semiconductor

(b) an intrinsic semiconductor

(c) p-type semiconductor

(d) n-type semiconductor

Concept: Electrical Properties - Applications of N-type and P-type Semiconductors
Chapter: [0.19] Semiconductors
5.7

The glass plate of refractive index 1.732 is to be used as a polarizer, its polarising angle is _______.

30°

45°

60°

90°

Concept: Polarisation
Chapter: [0.1] Wave Theory of Light
6 | Attempt Any Six
6.1

State the conditions to get constructive and destructive interference of light.

Concept: Interference of Light
Chapter: [0.11] Interference and Diffraction
6.2

State Ampere’s circuital law

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

Explain Ampere’s circuital law.

Concept: Ampere’s Circuital Law
Chapter: [0.14] Magnetic Effects of Electric Current
6.3

Draw the block diagram of a receiver in communication system

Concept: Elements of a Communication System
Chapter: [0.2] Communication Systems
6.4

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

Concept: Magnetisation and Magnetic Intensity
Chapter: [0.15] Magnetism
6.5

The electron in the hydrogen atom is moving with a speed of 2.3x106 m/s in an orbit of radius 0.53 Å. Calculate the period of revolution of the electron. (Π = 3.142)

Concept: Magnetic Dipole Moment of a Revolving Electron
Chapter: [0.15] Magnetism
6.6

A capacitor of capacitance 0.5 μF is connected to a source of alternating e.m.f. of frequency 100 Hz. What is the capacitive reactance? (Π = 3.142)

Concept: Reactance and Impedance
Chapter: [0.16] Electromagnetic Inductions
6.7

Calculate the de-Broglie wavelength of an electron moving with one-fifth of the speed of light.Neglect relativistic effects. (h = 6.63 xx 10^(-34) J.s, c= 3xx10^8m/s, mass of electron = 9 xx 10^(-31) kg)

Concept: de-Broglie Relation
Chapter: [0.18] Atoms, Molecules and Nuclei
6.8

For proton acceleration, a cyclotron is used in which a magnetic field of 1.4 Wb/m2 is applied. Find the time period for reversing the electric field between the two Ds.

Concept: Cyclotron Motion
Chapter: [0.1] Magnetic Fields Due to Electric Current
7 | Attempt Any Three
7.1

Explain with a neat circuit diagram how will you determine unknown resistance ‘X' by using meter bridge

Concept: Wheatstone Bridge
Chapter: [0.09] Current Electricity [0.13] Current Electricity
7.2

What is Zener diode?

Concept: Zener Diode as a Voltage Regulator
Chapter: [0.19] Semiconductors

Describe, with the help of a circuit diagram, the working of Zener diode as a voltage regulator.

Concept: Zener Diode as a Voltage Regulator
Chapter: [0.19] Semiconductors
7.3

In a biprism experiment, the light of wavelength 5200Å is used to get an interference pattern on the screen. The fringe width changes by 1.3 mm when the screen is moved towards biprism by 50 cm. Find the distance between two virtual images of the slit.

Concept: Interference of Light
Chapter: [0.11] Interference and Diffraction
7.4

The refractive indices of water and diamond are 4/3 and 2.42 respectively. Find the speed of light in water and diamond. (c = 3x108 m/s)

Concept: Huygens Principle
Chapter: [0.1] Wave Theory of Light
8 | Attempt Any One
8.1

Prove theoretically the relation between e.m.f. induced in a coil and rate of change of magnetic flux in electromagnetic induction.

Concept: Power in Ac Circuit: the Power Factor
Chapter: [0.16] Electromagnetic Inductions

A parallel plate air condenser has a capacity of 20µF. What will be a new capacity if:

1) the distance between the two plates is doubled?

2) a marble slab of dielectric constant 8 is introduced between the two plates?

Concept: The Parallel Plate Capacitor
Chapter: [0.12] Electrostatics
8.2

Draw a neat and labelled energy level diagram and explain Balmer series and Brackett series of spectral lines for the hydrogen atom.

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

The work function for a metal surface is 2.2eV. If the light of wavelength 5000Å is incident on the surface of the metal, find the threshold frequency and incident frequency. Will there be an emission of photoelectrons or not? (c = 3 x 108 m/ s, 1eV = 1.6x10-19 J , h = 6.63 x 10-34 J.s.)

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

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