# Physics All India Set 3 2016-2017 CBSE (Science) Class 12 Question Paper Solution

Physics [All India Set 3]
Date & Time: 14th March 2017, 12:30 pm
Duration: 3h

1

How does the angle of minimum deviation of a glass prism vary, if the incident violet light is replaced by red light? Give reason.

Concept: Refraction Through a Prism
Chapter: [6.01] Ray Optics and Optical Instruments
2

Name the phenomenon which shows the quantum nature of electromagnetic radiation.

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

What is the direction of induced currents in metal rings 1 and 2 when current I in the wire is increasing steadily? Concept: Lenz’S Law and Conservation of Energy
Chapter: [4.02] Electromagnetic Induction
4

In which directions do the electric and magnetic field vectors oscillate in an electromagnetic wave propagating along the x-axis?

Concept: Propagation of Electromagnetic Waves
Chapter: [10.01] Communication Systems
5

Nichrome and copper wires of same length and same radius are connected in series. Current I is passed through them. Which wire gets heated up more? Justify your answer.

Concept: Cells, Emf, Internal Resistance
Chapter: [2.01] Current Electricity
6

Write two properties of a material suitable for making a permanent magnet

Concept: Hysteresis Loop
Chapter: [3.01] Magnetism and Matter

Write two properties of a material suitable for making  an electromagnet.

Concept: Hysteresis Loop
Chapter: [3.01] Magnetism and Matter
7 | Attempt any one
7.1

Draw the intensity pattern for single slit diffraction.

Concept: Diffraction - Seeing the Single Slit Diffraction Pattern
Chapter: [6.02] Wave Optics

Draw the intensity pattern for double slit interference.

Concept: Diffraction - Seeing the Single Slit Diffraction Pattern
Chapter: [6.02] Wave Optics

State differences between interference and diffraction patterns.

Concept: Diffraction - Seeing the Single Slit Diffraction Pattern
Chapter: [6.02] Wave Optics
7.2

Unpolarised light is passed through a polaroid P1. When this polarised beam passes through another polaroid P2 and if the pass axis of P2 makes angle θ with the pass axis of P1, then write the expression for the polarised beam passing through P2. Draw a plot showing the variation of intensity when θ varies from 0 to 2π.

Concept: Polarisation
Chapter: [6.02] Wave Optics
8

Why does current in a steady state not flow in a capacitor connected across a battery? However momentary current does flow during charging or discharging of the capacitor. Explain.

Concept: Ac Voltage Applied to a Series Lcr Circuit
Chapter: [4.01] Alternating Current
9

The ground state energy of hydrogen atom is – 13∙6 eV. If an electron makes a transition from an energy level – 1∙51 eV to – 3∙4 eV, calculate the wavelength of the spectral line emitted and name the series of hydrogen spectrum to which it belongs.

Concept: Hydrogen Spectrum
Chapter: [8.02] Atoms
10

Find the condition under which the charged particles moving with different speeds in the presence of electric and magnetic field vectors can be used to select charged particles of a particular speed.

Concept: Motion in a Magnetic Field
Chapter: [3.02] Moving Charges and Magnetism
11 | Attempt any one
11.1

Monochromatic light of wavelength 589 nm is incident from air on a water surface. If µ for water is 1.33, find the wavelength, frequency and speed of the refracted light.

Concept: Refraction
Chapter: [6.01] Ray Optics and Optical Instruments
11.2

A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.

Concept: Reflection of Light by Spherical Mirrors
Chapter: [6.01] Ray Optics and Optical Instruments
12 | Attempt any one
12.1

Define mutual inductance and write its S.I. units

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

Derive an expression for the mutual inductance of two long co-axial solenoids of same length wound one over the other,

Concept: Solenoid and the Toroid - the Solenoid
Chapter: [3.02] Moving Charges and Magnetism
12.2

Define self-inductance of a coil.

Concept: Solenoid and the Toroid - the Solenoid
Chapter: [3.02] Moving Charges and Magnetism

Obtain an expression for the energy stored in a solenoid of self-inductance ‘L’ when the current through it grows from zero to ‘I’.

Concept: Solenoid and the Toroid - the Solenoid
Chapter: [3.02] Moving Charges and Magnetism
13

Write the principle of working of a metre bridge

Concept: Metre Bridge
Chapter: [2.01] Current Electricity

In a metre bridge, the balance point is found at a distance l1 with resistances R and S as shown in the figure.An unknown resistance X is now connected in parallel to the resistance S and the balance point is found at a distance l2. Obtain a formula for X in terms of l1, l2 and S. Concept: Metre Bridge
Chapter: [2.01] Current Electricity
14

Draw a circuit diagram of a transistor amplifier in CE configuration.

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

Derive an expression for voltage gain of the amplifier and hence show that the output voltage is in opposite phase with the input voltage.

Concept: Junction Transistor - Transistor as an Amplifier (Ce-configuration)
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
15

The potential difference applied across a given resistor is altered so that the heat produced per second increases by a factor of 9. By what factor does the applied potential difference change?

Concept: Electric Potential Difference
Chapter: [1.01] Electrostatic Potential and Capacitance

In the figure shown, an ammeter A and a resistor of 4 Ω are connected to the terminals of the source. The emf of the source is 12 V having an internal resistance of 2 Ω. Calculate the voltmeter and ammeter readings. Concept: Electric Potential Difference
Chapter: [1.01] Electrostatic Potential and Capacitance
16

Draw a block diagram of generalized communication system.

Concept: Elements of a Communication System
Chapter: [10.01] Communication Systems

Write the functions of the following in communication systems:

Transmitter

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

Write the functions of each of the following in communication system : Channel

Concept: Elements of a Communication System
Chapter: [10.01] Communication Systems

Write the functions of the following in communication systems:

Concept: Basic Terminology Used in Electronic Communication Systems
Chapter: [10.01] Communication Systems
17

Draw a labelled ray diagram showing the formation of a final image by a compound microscope at least distance of distinct vision

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

You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct a compound microscope?

 Lenses Power (D) Aperture (cm) L1 3 8 L2 6 1 L3 10 1
Concept: Optical Instruments - The Microscope
Chapter: [6.01] Ray Optics and Optical Instruments

Define resolving power of a microscope and write one factor on which it depends

Concept: Optical Instruments - The Microscope
Chapter: [6.01] Ray Optics and Optical Instruments
18

The following graph shows the variation of photocurrent for a photosensitive metal : (a) Identify the variable X on the horizontal axis.

(b) What does the point A on the horizontal axis represent?

(c) Draw this graph for three different values of frequencies of incident radiation v1, v2 and v3 (v1 > v2 > v3) for same intensity.

(d) Draw this graph for three different values of intensities of incident radiation I1, I2 and I3 (I1 > I2 > I3) having same frequency.

Concept: Experimental Study of Photoelectric Effect
Chapter: [7.01] Dual Nature of Radiation and Matter
19

Two identical parallel plate capacitors A and B are connected to a battery of V volts with the switch S closed. The switch is now opened and the free space between the plates of the capacitors is filled with a dielectric of dielectric constant K. Find the ratio of the total electrostatic energy stored in both capacitors before and after the introduction of the dielectric. Concept: Capacitors and Capacitance
Chapter: [1.01] Electrostatic Potential and Capacitance
20

How is amplitude modulation achieved?

Concept: Amplitude Modulation
Chapter: [10.01] Communication Systems

The frequencies of two side bands in an AM wave are 640 kHz and 660 kHz respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation?

Concept: Amplitude Modulation
Chapter: [10.01] Communication Systems
21

In the following diagram 'S' is a semiconductor. Would you increase or decrease the value of R to keep the reading of the ammeter A constant when S is heated? Give reason for your answer. Concept: Semiconductor Diode
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits

With the help of a neat circuit diagram, explain the working of a photodiode.

Concept: Special Purpose P-n Junction Diodes
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits

Draw its I – V characteristics of photodiode

Concept: Semiconductor Diode
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
22

State Biot – Savart law.

Concept: Magnetic Field Due to a Current Element, Biot-Savart Law
Chapter: [3.02] Moving Charges and Magnetism

Express  Biot – Savart law in the vector form.

Concept: Magnetic Field Due to a Current Element, Biot-Savart Law
Chapter: [3.02] Moving Charges and Magnetism

Two identical circular coils, P and Q each of radius R, carrying currents 1 A and √3A respectively, are placed concentrically and perpendicular to each other lying in the XY and YZ planes. Find the magnitude and direction of the net magnetic field at the centre of the coils.

Concept: Magnetic Field on the Axis of a Circular Current Loop
Chapter: [3.02] Moving Charges and Magnetism
23

Asha's mother read an article in the newspaper about a disaster that took place at Chernobyl. She could not understand much from the articles and asked a few questions from Asha regarding the article. Asha tried to answer her mother's questions based on what she learnt in Class XII Physics.

(a) What was the installation at Chernobyl where the disaster took place? What according to you, was the cause of this disaster?

(b) Explain the process of release of energy in the installation at Chernobyl.

(c) What according to you, were the values displayed by Asha and her mother?

Concept: Mass-energy and Nuclear Binding Energy - Mass - Energy
Chapter: [8.01] Nuclei
24 | Attempt any one
24.1

A device 'X' is connected to an ac source V = V0 sin ωt. The variation of voltage, current and power in one cycle is shown in the following graph: (a) Identify the device 'X'.
(b) Which of the curves A, B and C represent the voltage , current and the power consumed in the circuit? Justify your answer.
(c) How does its impedance vary with frequency of the ac source? Show graphically.
(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.

Concept: Ac Voltage Applied to a Resistor
Chapter: [4.01] Alternating Current
24.2

Draw a labelled diagram of an ac generator.

Concept: AC Generator
Chapter: [4.02] Electromagnetic Induction

Obtain the expression for the emf induced in the rotating coil of N turns each of cross-sectional area A, in the presence of a magnetic field vecB .

Concept: AC Generator
Chapter: [4.02] Electromagnetic Induction

A horizontal straight wire 10 m long extending from east to west is falling with a speed of 5.0 m s−1, at right angles to the horizontal component of the earth’s magnetic field, 0.30 × 10−4 Wb m−2.

(a) What is the instantaneous value of the emf induced in the wire?

(b) What is the direction of the emf?

(c) Which end of the wire is at the higher electrical potential?

Concept: AC Generator
Chapter: [4.02] Electromagnetic Induction
25 | Attempt any one
25.1

Define the term wave front.

Concept: Huygens Principle
Chapter: [6.02] Wave Optics

Use Huygens' principle to verify the laws of refraction.

Concept: Huygens Principle
Chapter: [6.02] Wave Optics

How is linearly polarised light obtained by the process of scattering of light. Find the Brewster angle for air – glass interface, when the refractive index of glass = 1.5.

Concept: Plane Polarised Light
Chapter: [6.02] Wave Optics
25.2

Two thin convex lenses L1 and L2 of focal lengths f1 and f2, respectively, are placed coaxially in contact. An object is placed at a point beyond the focus of lens L1. Draw a ray diagram to show the image formation by the combination and hence derive the expression for the focal length of the combined system.

Concept: Refraction at Spherical Surfaces and by Lenses - Combination of Thin Lenses in Contact
Chapter: [6.01] Ray Optics and Optical Instruments

A ray of light passing from air through an equilateral glass prism undergoes minimum deviation when the angle of incidence is 3/4 th of the angle of prism. Calculate the speed of light in the prism.

Concept: Refraction Through a Prism
Chapter: [6.01] Ray Optics and Optical Instruments
26 | Attempt any one
26.1

(a) Derive an expression for the electric field E due to a dipole of length '2a' at a point distant r from the centre of the dipole on the axial line.
(b) Draw a graph of E versus r for r >> a.
(c) If this dipole were kept in a uniform external electric field E0, diagrammatically represent the position of the dipole in stable and unstable equilibrium and write the expressions for the torque acting on the dipole in both the cases.

Concept: Electric Field Lines
Chapter: [1.02] Electric Charges and Fields
26.2

Use Gauss's law to find the electric field due to a uniformly charged infinite plane sheet. What is the direction of field for positive and negative charge densities?

Concept: Uniformly Charged Infinite Plane Sheet and Uniformly Charged Thin Spherical Shell (Field Inside and Outside)
Chapter: [1.02] Electric Charges and Fields

An infinitely large thin plane sheet has a uniform surface charge density +σ. Obtain the expression for the amount of work done in bringing a point charge q from infinity to a point, distant r, in front of the charged plane sheet.

Concept: Uniformly Charged Infinite Plane Sheet and Uniformly Charged Thin Spherical Shell (Field Inside and Outside)
Chapter: [1.02] Electric Charges and Fields

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