Physics Set 1 2018-2019 HSC Science (Electronics) 12th Board Exam Question Paper Solution

Physics [Set 1]
Date & Time: 25th February 2019, 11:00 am
Duration: 3h

SECTION - A
 1

When a sparingly soluble substance like alcohol is dissolved in water, surface tension of water

increases

decreases

remains constant

becomes infinite

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

The specific heat capacity of water is

8R

7/8R

9R

9/7R

Concept: Specific Heat Capacities - Gases
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 3

The electric field intensity outside the charged conducting sphere of radius ‘R’, placed in a medium of permittivity ∈ at a distance ‘r’ from the centre of the sphere in terms of surface charge density σ is

σ/∈ (R/r)^2

σ/∈ (r/R)^2

σ/∈ (R^2/r^2)^2

σ/∈ (r^2/R^2)^2

Concept: Applications of Gauss’s Law
Chapter: [0.12] Electrostatics
 4

An electron of energy 150 eV has wavelength of 10-10m. The wavelength of a 0.60 keV electron is?

0.50 Å

0.75 Å

1.2 Å

1.5 Å

Concept: de-Broglie Relation
Chapter: [0.18] Atoms, Molecules and Nuclei
 5

What is the value of tangential acceleration in U.C.M.?

Concept: Angular Acceleration
Chapter: [0.01] Circular Motion
 6

What happens to a ferromagnetic substance heated above Curie temperature ?

Concept: Curie Temperature
Chapter: [0.15] Magnetism
 7

At which position of the plane of the rotating coil with the direction of magnetic field, the e.m.f. induced in the coil is maximum?

Concept: Coil Rotating in Uniform Magnetic Induction
Chapter: [0.16] Electromagnetic Inductions
 8

Name the logic gate which generated high output when at least one input is high.

Concept: Digital Electronics and Logic Gates
Chapter: [0.19] Semiconductors
SECTION - B
 9

In Young’s experiment interference bands were produced on a screen placed at 150 cm from two slits, 0.15 mm apart and illuminated by the light of wavelength 6500 Å. Calculate the fringe width.

Concept: Interference of Light Waves and Young’S Experiment
Chapter: [0.11] Interference and Diffraction
 10

The susceptibility of magnesium at 300 K is 1.2 x 10 -5 . What will be its susceptibility at 200 K.

Concept: Curie Temperature
Chapter: [0.15] Magnetism
 11 | Attempt any one:
 11.1

The length of the second’s pendulum in a clock is increased to 4 times its initial length. Calculate the number of oscillations completed by the new pendulum in one minute.

Concept: Periodic and Oscillatory Motions
Chapter: [0.04] Oscillations [0.05] Oscillations
OR
 11.2

A body of mass 1 kg is mafe to oscillate on a spring of force constant 16 N/m. Calculate (a) Angular frequency, (b) Frequency of vibrations.

Concept: Periodic and Oscillatory Motions
Chapter: [0.04] Oscillations [0.05] Oscillations
 12

Define the capacitance of a capacitor and its SI unit.

Concept: The Parallel Plate Capacitor
Chapter: [0.12] Electrostatics
 13

Define radius of gyration. Write its physical significance.

Concept: Definition of M.I., K.E. of Rotating Body
Chapter: [0.03] Angular Momentum
 14

Distinguish between p-type and n-type semiconductors.

Concept: Electrical Properties - Applications of N-type and P-type Semiconductors
Chapter: [0.19] Semiconductors
 15

Explain the terms (a) Transducer and (b) Attenuation in communication system.

Concept: Elements of a Communication System
Chapter: [0.2] Communication Systems
SECTION - C
 16

Obtain expressions of energy of a particle at different positions in the vertical circular motion .

Concept: Vertical Circular Motion Due to Earth’s Gravitation
Chapter: [0.01] Circular Motion
 17

Define binding energy and obtain an expression for binding energy of a satellite revolving in a circular orbit round the earth.

Concept: Binding Energy and Escape Velocity of a Satellite
Chapter: [0.02] Gravitation
 18

State Hooke’s law. Define the elastic limit and modulus of elasticity.

Concept: Hooke’s Law
Chapter: [0.05] Elasticity
 19

Obtain an expression for the rise of a liquid in a capillary tube.

Concept: Capillarity and Capillary Action
Chapter: [0.02] Mechanical Properties of Fluids [0.06] Surface Tension
 20

Explain the reflection of transverse and longitudinal waves from a denser medium and a rared medium.

Concept: Reflection of Transverse and Longitudinal Waves
Chapter: [0.07] Wave Motion
 21

What is photoelectri effect ? Defin (i) Stopping potential (ii) Photoelectric work function.

Concept: Photoelectric Effect - Hertz’S Observations
Chapter: [0.17] Electrons and Photons
 22

What is perfectly black body ? Explain Ferry’s black body.

Concept: Qualitative Ideas of Blackbody Radiation
Chapter: [0.09] Kinetic Theory of Gases and Radiation
 23

When a resistor of 5Ω is connected across the cell, its terminal potential difference is balanced by 150 cm of potentiometer wire and when a resistance of 10 Ω is connected across the cell, the terminal potential difference is balanced by 175 cm same potentiometer wire. Find the balancing length when the cell is in open circuit and the internal resistance of the cell.

Concept: Potentiometer
Chapter: [0.09] Current Electricity [0.13] Current Electricity
 24

A cyclotron is used to accelerate protons to a kinetic energy of 5 MeV. If the strength of magnetic field in the cyclotron is 2T, find the radius and the frequency needed for the applied alternating voltage of the cyclotron. (Given : Velocity of proton= 3xx10^7 m//s)

Concept: Motion in Combined Electric and Magnetic Fields - Cyclotron
Chapter: [0.14] Magnetic Effects of Electric Current
 25

Assuming expression for impedance in a parallel resonant circuit, state the conditions for parallel resonance. Define resonant frequency and obtain an expression for it.

Concept: Forced Oscillations and Resonance
Chapter: [0.08] Stationary Waves
 26 | Attempt any one:
 26.1

Using an expression for energy of electron, obtain the Bohr’s formula for hydrogen spectral lines.

Concept: Hydrogen Spectrum
Chapter: [0.18] Atoms, Molecules and Nuclei
 26.2

State the law of radioactive decay. hence derive the relation N = Noe-λt . Represent it graphically.

Chapter: [0.18] Atoms, Molecules and Nuclei
SECTION - D
 27 | Attempt any two:
 27.1
 27.1.1

Show that even as well as odd harmonics are present as overtones in the case of an air column vibrating in a pipe open at both the ends.

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
 27.1.2

A wheel of moment of inertia 1 kg.m2 is rotating at a speed of 30 rad/s. Due to friction on the axis, it comes to rest in 10 minutes. Calculate the average torque of the friction.

Concept: Study of Vibrations of Air Columns
Chapter: [0.06] Superposition of Waves [0.08] Stationary Waves
OR
 27.2
 27.2.1

Explain the formation of stationary waves by analytical method. Show that nodes and antinodes are equally spaced in stationary waves.

Concept: Formation of Stationary Waves on String
Chapter: [0.08] Stationary Waves
 27.2.2

The radius of gyration of a body about an axis, at a distance of 0.4 m from its centre of mass is 0.5 m. Find its radius of gyration about a parallel axis passing through its centre of mass.

Concept: Definition of M.I., K.E. of Rotating Body
Chapter: [0.03] Angular Momentum
 28 | Attempt any one:
 28.1
 28.1.1

Obtan an expression for potential energy of a particle performing S.H.M. What is the value of potential energy at (i) Mean position, and (ii) Extreme position

Concept: K.E.(Kinetic Energy) and P.E.(Potential Energy) in S.H.M.
Chapter: [0.04] Oscillations
 28.1.2

A stretched sonometer wire is in unison with a tuning fork. When the length of the wire is increased by 5%, the number of beats heard per second is 10. Find the frequency of the tuning fork.

Concept: Study of Vibrations in a Finite Medium
Chapter: [0.08] Stationary Waves
OR
 28.2
 28.2.1

From differential equation of linear S.H.M., obtain an expression for acceleration, velocity and displacement of a particle performing S.H.M.

Concept: Differential Equation of Linear S.H.M.
Chapter: [0.04] Oscillations [0.05] Oscillations
 28.2.2

A sonometer wire 1 metre long weighing 2 g is in resonance with a tuning fork of frequency 300 Hz. Find tension in the sonometer wire.

Concept: Study of Vibrations in a Finite Medium
Chapter: [0.08] Stationary Waves
 29 | Attempt any one of the following
 29.1
 29.1.1

Explain refraction of light on the basis of wave theory. Hence prove the laws of refraction

Concept: Reflection and Refraction of Plane Wave at a Plane Surface Using Wave Fronts
Chapter: [0.1] Wave Theory of Light
 29.1.2

Two coherent sources of light having intensity ratio 81 : 1 produce interference fringes. Calculate the ratio of intensities at the maxima and minima in the interference pattern.

Concept: Interference of Light Waves and Young’S Experiment
Chapter: [0.11] Interference and Diffraction
OR
 29.2
 29.2.1

State Brewster’s law and show that when light is incident at polarizing angle the reflected and refracted rays are mutually perpendicular to each other.

Concept: Brewster's Law
Chapter: [0.1] Wave Theory of Light
 29.2.2

Monochromatic light of wavelength 4300 Å falls on a slit of width ‘a’. For what value of ‘a’ the first maximum falls at 30° ?

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

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