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# Question Paper Solutions - Physics 2016 - 2017-CBSE 12th-Class 12 CBSE (Central Board of Secondary Education)

SubjectPhysics
Year2016 - 2017 (March)

#### Alternate Sets

Marks: 70
[1]1

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.

Chapter: [11] Current Electricity
Concept: Cells, Emf, Internal Resistance
[1]2

Do electromagnetic waves carry energy and momentum ?

Chapter: [5.01] Electromagnetic Waves
Concept: Electromagnetic Waves
[1]3

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

Chapter: [6.01] Ray Optics and Optical Instruments
Concept: Refraction Through a Prism
[1]4

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

Chapter: [14] Electromagnetic Waves
Concept: Electromagnetic Spectrum
[1]5

Predict the polarity of the capacitor in the situation described below :

Chapter: [3.02] Magnetism and Matter
Concept: The Bar Magnet
[2]6 | Attempt any one
[2]6.1

Draw the intensity pattern for single slit diffraction.

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

Draw the intensity pattern for double slit interference.

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

State differences between interference and diffraction patterns.

Chapter: [6.02] Wave Optics
Concept: Diffraction - Seeing the Single Slit Diffraction Pattern
[2]6.2

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.

Chapter: [6.02] Wave Optics
Concept: Polarisation
[2]7

Identify the electromagnetic waves whose wavelengths vary as:

(a) 10–12 m < λ < 10–8 m

(b) 10–3 m < λ < 10–1 m

Write one use for each.

Chapter: [5.01] Electromagnetic Waves
Concept: Electromagnetic Waves
[2]8

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.

Chapter: [3.01] Moving Charges and Magnetism
Concept: Motion in a Magnetic Field
[2]9

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?

Chapter: [8.01] Atoms
Concept: The Line Spectra of the Hydrogen Atom
[2]10

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

Chapter: [3.02] Magnetism and Matter
Concept: Hysteresis Loop

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

Chapter: [3.02] Magnetism and Matter
Concept: Hysteresis Loop
[3]11

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?

Chapter: [4.01] Effects of Current
Concept: Electric Potential Difference

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.

Chapter: [4.01] Effects of Current
Concept: Electric Potential Difference
[3]12

How is amplitude modulation achieved?

Chapter: [10.01] Communication Systems
Concept: Amplitude Modulation

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?

Chapter: [10.01] Communication Systems
Concept: Amplitude Modulation
[3]13

In the following diagram, is the junction diode forward biased or reverse biased ?

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

Draw the circuit diagram of a full wave rectifier along with the input and output waveforms

Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
Concept: Diode as a Rectifier
[3]14

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?

Chapter: [7] Dual Nature of Radiation and Matter
Concept: Electron Emission

Write Einstein's photoelectric equation and mention which important features in photoelectric effect can be explained with the help of this equation.

The maximum kinetic energy of the photoelectrons gets doubled when the wavelength of light incident on the surface changes from λ1 to λ2. Derive the expressions for the threshold wavelength λ0 and work function for the metal surface.

Chapter: [17] Electrons and Photons
Concept: Einstein’s Equation - Particle Nature of Light
[3]15

Monochromatic light of wavelength 589 nm is incident from air on a water surface. What are the wavelength, frequency and speed of (a) reflected, and (b) refracted light? Refractive index of water is 1.33.

Chapter: [6.02] Wave Optics
Concept: Introduction of Wave Optics

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.

Chapter: [9] Ray Optics
Concept: Reflection of Light by Spherical Mirrors
[3]16 | Attempt any one
[3]16.1

Define mutual inductance and write its S.I. units

Chapter: [4.01] Electromagnetic Induction
Concept: Inductance - Mutual Inductance

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

Chapter: [3.01] Moving Charges and Magnetism
Concept: Solenoid and the Toroid - the Solenoid
[3]16.2

Define self-inductance of a coil.

Chapter: [3.01] Moving Charges and Magnetism
Concept: Solenoid and the Toroid - the Solenoid
[3]17

Write the principle of working of a metre bridge

Chapter: [2] Current Electricity
Concept: Metre Bridge

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.

Chapter: [2] Current Electricity
Concept: Metre Bridge
[3]18

Draw a block diagram of generalized communication system.

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

Write the functions of the following in communication systems:

Transmitter

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

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

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

Write the functions of the following in communication systems:

Chapter: [10.01] Communication Systems
Concept: Basic Terminology Used in Electronic Communication Systems
[3]19

Write the functions of the three segments of a transistor.

Chapter: [19] Semiconductors
Concept: Transistor and Characteristics of a Transistor

The figure shows the input waveforms A and B for ‘AND’ gate. Draw the output waveform and write the truth table for this logic gate.

Chapter: [19] Semiconductors
Concept: Transistor and Characteristics of a Transistor
[3]20

Draw a ray diagram depicting the formation of the image by an astronomical telescope in normal adjustment.

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

You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope ? Give reason

 Lenses Power (D) Aperture (cm) L1 3 8 L2 6 1 L3 10 1
Chapter: [6.01] Ray Optics and Optical Instruments
Concept: Optical Instruments - Telescope
[3]21

State Biot – Savart law.

Chapter: [12] Magnetic Effect of Electric Current
Concept: Magnetic Field Due to a Current Element, Biot-Savart Law

Express  Biot – Savart law in the vector form.

Chapter: [12] Magnetic Effect of Electric Current
Concept: Magnetic Field Due to a Current Element, Biot-Savart Law

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.

Chapter: [3.01] Moving Charges and Magnetism
Concept: Magnetic Field on the Axis of a Circular Current Loop
[3]22

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.

Chapter: [1.02] Electrostatic Potential, Potential Energy and Capacitance
Concept: Capacitors and Capacitance
[4]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?

Chapter: [8.02] Nuclei
Concept: Mass-energy and Nuclear Binding Energy - Mass - Energy
[5]24 | Attempt any one :
[5]24.1

(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.

Chapter: [1.01] Electric Charges and Fields
Concept: Electric Field Lines
[5]24.2

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?

Chapter: [1.01] Electric Charges and Fields
Concept: Uniformly Charged Infinite Plane Sheet and Uniformly Charged Thin Spherical Shell (Field Inside and Outside)

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.

Chapter: [1.01] Electric Charges and Fields
Concept: Uniformly Charged Infinite Plane Sheet and Uniformly Charged Thin Spherical Shell (Field Inside and Outside)
[5]25 | Attempt any one :
[5]25.1

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.

Chapter: [4.02] Alternating Current
Concept: Ac Voltage Applied to a Resistor
[5]25.2

Draw a labelled diagram of an ac generator.

Chapter: [4.01] Electromagnetic Induction
Concept: Ac Generator

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 .

Chapter: [4.01] Electromagnetic Induction
Concept: Ac Generator

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?

Chapter: [4.01] Electromagnetic Induction
Concept: Ac Generator
[5]26 | Attempt any one :
[5]26.1

Define the term wave front.

Chapter: [6.02] Wave Optics
Concept: Huygens Principle

Use Huygens' principle to verify the laws of refraction.

Chapter: [6.02] Wave Optics
Concept: Huygens Principle

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.

Chapter: [6.02] Wave Optics
Concept: Plane Polarised Light
[5]26.2

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.

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

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.

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