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# Physics Delhi Set 1 2015-2016 CBSE (Arts) Class 12 Question Paper Solution

Physics [Delhi Set 1]
Marks: 70Date: 2016-03-05
Duration: 3h

[1]1

A point charge +Q is placed at point O, as shown in the figure. Is the potential difference VAVB positive, negative or zero?

Concept: Potential Due to a Point Charge
Chapter: [1.01] Electrostatic Potential and Capacitance
[1]2

How does the electric flux due to a point charge enclosed by a spherical Gaussian surface get affected when its radius is increased?

Concept: Electric Flux
Chapter: [1.02] Electric Charges and Fields
[1]3

Write the underlying principle of a moving coil galvanometer.

Concept: Moving Coil Galvanometer
Chapter: [3.02] Moving Charges and Magnetism
[1]4

Why are microwaves considered suitable for radar systems used in aircraft navigation?

Concept: Electromagnetic Spectrum
Chapter: [5.01] Electromagnetic Waves
[1]5

Define 'quality factor' of resonance in a series LCR circuit. What is its SI unit?

Concept: Ac Voltage Applied to a Series Lcr Circuit
Chapter: [4.01] Alternating Current
[2]6

Explain the terms Attenuation used in Communication System.

Concept: Basic Terminology Used in Electronic Communication Systems
Chapter: [10.01] Communication Systems

Explain the terms Demodulation used in Communication System.

Concept: Basic Terminology Used in Electronic Communication Systems
Chapter: [10.01] Communication Systems
[2]7

Plot a graph showing variation of de Broglie wavelength λ versus 1/sqrtV , where V is accelerating potential for two particles A and B, carrying the same charge but different masses m1, m2 (m1 > m2). Which one of the two represents a particle of smaller mass and why?

Concept: de-Broglie Relation
Chapter: [7.01] Dual Nature of Radiation and Matter
[2]8 | Attempt Any One
[2]8.1

A nucleus with mass number A = 240 and BE/A = 7.6 MeV breaks into two fragments, each of A = 120 with BE/A = 8.5 MeV. Calculate the released energy.

Concept: Atomic Masses and Composition of Nucleus
Chapter: [8.01] Nuclei
[2]8.2

Calculate the energy in fusion reaction:

""_1^2H+_1^2H->_2^3He+n, where BE of ""_1^2H23He=7.73MeV" data-mce-style="position: relative;">=2.2323He=7.73MeV MeV and of ""_2^3He=7.73 MeV

Concept: Nuclear Energy - Nuclear Fusion – Energy Generation in Stars
Chapter: [8.01] Nuclei
[2]9

Two cells of emfs 1.5 V and 2.0 V,  having internal resistances 0.2 Ω and 0.3 Ω, respectively, are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.

Concept: Cells, Emf, Internal Resistance
Chapter: [2.01] Current Electricity
[2]10

State Brewster's law.

Concept: Brewster's Law
Chapter: [6.02] Wave Optics

The value of Brewster's angle for a transparent medium is different for light of different colours. Give reason.

Concept: Brewster's Law
Chapter: [6.02] Wave Optics
[3]11

A charge is distributed uniformly over a ring of radius 'a'. Obtain an expression for the electric intensity E at a point on the axis of the ring. Hence, show that for points at large distance from the ring, it behaves like a point charge.

Concept: Electric Field Due to a Point Charge
Chapter: [1.02] Electric Charges and Fields
[3]12

Write three characteristic features in photoelectric effect that cannot be explained on the basis of wave theory of light, but can be explained only using Einstein's equation.

Concept: Photoelectric Effect - Hertz’S Observations
Chapter: [7.01] Dual Nature of Radiation and Matter
[3]13

(a) Write the expression for the magnetic force acting on a charged particle moving with velocity v in the presence of magnetic field B.

Concept: Magnetic Force
Chapter: [3.02] Moving Charges and Magnetism

A neutron, an electron and an alpha particle, moving with equal velocities, enter a uniform magnetic field going into the plane of the paper, as shown. Trace their paths in the field and justify your answer.

Concept: Force on a Moving Charge in Uniform Magnetic and Electric Fields
Chapter: [3.02] Moving Charges and Magnetism
[3]14

Define mutual inductance.

Concept: Inductance - Mutual Inductance
Chapter: [4.02] Electromagnetic Induction
[3]15

Two parallel-plate capacitors X and Y have the same area of plates and same separation between them. X has air between the plates, while Y contains a dielectric medium of εr = 4.

(i) Calculate capacitance of each capacitor if the equivalent capacitance of the combination is 4 μF.

(ii) Calculate the potential difference between the plates X and Y.

(iii) Estimate the ratio of electrostatic energies stored in X and Y.

Concept: Capacitance of a Parallel Plate Capacitor with and Without Dielectric Medium Between the Plates
Chapter: [1.01] Electrostatic Potential and Capacitance
[3]16

Two long, straight, parallel conductors carry steady currents, I1 and I2, separated by a distance d. If the currents are flowing in the same direction, show how the magnetic field set up in one produces an attractive force on the other? Obtain the expression for this force. Hence, define one ampere.

Concept: Magnetic Force
Chapter: [3.02] Moving Charges and Magnetism
[3]17 | Attempt Any One
[3]17.1

How are em waves produced by oscillating charges?

Concept: Electromagnetic Waves
Chapter: [5.01] Electromagnetic Waves

Draw a sketch of linearly polarized em waves propagating in the Z-direction. Indicate the directions of the oscillating electric and magnetic fields.

Concept: Electromagnetic Waves
Chapter: [5.01] Electromagnetic Waves
[3]17.2

Write Maxwell's generalization of Ampere's circuital law. Show that in the process of charging a capacitor, the current produced within the plates of the capacitor is I=varepsilon_0 (dphi_E)/dt,where ΦE is the electric flux produced during charging of the capacitor plates.

Concept: Ampere’s Circuital Law
Chapter: [3.02] Moving Charges and Magnetism
[3]18

Explain any two factors that justify the need of modulating a low-frequency signal.

Concept: Amplitude Modulation
Chapter: [10.01] Communication Systems

Write two advantages of frequency modulation over amplitude modulation.

Concept: Amplitude Modulation
Chapter: [10.01] Communication Systems
[3]19

Write the functions of three segments of a transistor.

Concept: Junction Transistor - Transistor as an Amplifier (Ce-configuration)
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[3]20

Calculate the distance of an object of height h from a concave mirror of radius of curvature 20 cm, so as to obtain a real image of magnification 2. Find the location of the image also.

Concept: Ray Optics - Mirror Formula
Chapter: [6.01] Ray Optics and Optical Instruments

Using mirror formula, explain why does a convex mirror always produce a virtual image.

Concept: Ray Optics - Mirror Formula
Chapter: [6.01] Ray Optics and Optical Instruments
[3]21

(i) State Bohr's quantization condition for defining stationary orbits. How does the de Broglie hypothesis explain the stationary orbits?

(ii) Find the relation between three wavelengths λ1, λ2 and λ3 from the energy-level diagram shown below.

Concept: Bohr'S Model for Hydrogen Atom
Chapter: [8.02] Atoms
[3]22

Draw a schematic ray diagram of a reflecting telescope showing how rays coming from a distant object are received at the eyepiece.

Concept: Optical Instruments - Telescope
Chapter: [6.01] Ray Optics and Optical Instruments

Write two important advantages of reflecting telescope over a refracting telescope.

Concept: Optical Instruments - Telescope
Chapter: [6.01] Ray Optics and Optical Instruments
[4]23

Meeta's father was driving her to school. At the traffic signal, she noticed that each traffic light was made of many tiny lights instead of a single bulb. When Meeta asked this question to her father, he explained the reason for this.

Answer the following questions based on above information:

(i) What were the values displayed by Meeta and her father?

(ii) What answer did Meeta's father give?

(iii) What are the tiny lights in traffic signals called and how do these operate?

Concept: Special Purpose P-n Junction Diodes
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[5]24 | Attempt Any One
[5]24.1

An a.c. source of voltage V = V0 sin ωt is connected to a series combination of L, C, and R. Use the phasor diagram to obtain the expression for an impedance of a circuit and the phase angle between voltage and current. Find the condition when current will be in phase with the voltage. What is the circuit in this condition called?

Concept: Power in Ac Circuit: the Power Factor
Chapter: [4.01] Alternating Current

In a series LR circuit, XL = R and power factor of the circuit is P1. When capacitor with capacitance C such that XL = XC is put in series, the power factor becomes P2. Calculate P1/P2

Concept: Power in Ac Circuit: the Power Factor
Chapter: [4.01] Alternating Current
[5]24.2

Write the function of a transformer.

Concept: Transformers
Chapter: [4.01] Alternating Current

State the principle of transformer working with the help of a diagram

Concept: Transformers
Chapter: [4.01] Alternating Current

Mention various energy losses in transformer device

Concept: Transformers
Chapter: [4.01] Alternating Current

The primary coil of an ideal step-up transformer has 100 turns and the transformation ratio is also 100. The input voltage and power are 220 V and 1100 W, respectively. Calculate the

(a) number of turns in secondary
(b) current in the primary
(c) a voltage across secondary
(d) current in secondary
(e) power in secondary

Concept: Transformers
Chapter: [4.01] Alternating Current
[5]25 | Attempt Any One
[5]25.1

(i) In Young's double-slit experiment, deduce the condition for (a) constructive and (b) destructive interferences at a point on the screen. Draw a graph showing variation of intensity in the interference pattern against position 'x' on the screen.

(b) Compare the interference pattern observed in Young's double-slit experiment with single-slit diffraction pattern, pointing out three distinguishing features.

Concept: Interference of Light Waves and Young’S Experiment
Chapter: [6.02] Wave Optics
[5]25.2

Plot a graph to show the variation of the angle of deviation as a function of the angle of incidence for light passing through a prism. Derive an expression for the refractive index of the prism in terms of angle of minimum deviation and angle of the prism.

Concept: Dispersion by a Prism
Chapter: [6.01] Ray Optics and Optical Instruments

What is a dispersion of light

Concept: Dispersion by a Prism
Chapter: [6.01] Ray Optics and Optical Instruments

What is the cause of dispersion of light

Concept: Dispersion by a Prism
Chapter: [6.01] Ray Optics and Optical Instruments

A ray of light incident normally on one face of a right isosceles prism is totally reflected, as shown in fig. What must be the minimum value of refractive index of glass? Give relevant calculations.

Concept: Dispersion by a Prism
Chapter: [6.01] Ray Optics and Optical Instruments
[5]26 | Attempt Any One
[5]26.1

Define the term drift velocity.

Concept: Drift of Electrons and the Origin of Resistivity
Chapter: [2.01] Current Electricity

On the basis of electron drift, derive an expression for resistivity of a conductor in terms of number density of free electrons and relaxation time. On what factors does resistivity of a conductor depend?

Concept: Drift of Electrons and the Origin of Resistivity
Chapter: [2.01] Current Electricity

Why alloys like constantan and manganin are used for making standard resistors?

Concept: Drift of Electrons and the Origin of Resistivity
Chapter: [2.01] Current Electricity
[5]26.2

In the following potentiometer circuit, AB is a uniform wire of length 1 m and resistance 10 Ω. Calculate the potential gradient along the wire and balance length AO (= l).

Concept: Potential Difference and Emf of a Cell
Chapter: [2.01] Current Electricity

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