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# Physics Foreign Set 1 2013-2014 CBSE (Arts) Class 12 Question Paper Solution

Physics
Foreign Set 1
2013-2014 March
Marks: 70

[1]1

A flexible wire of irregular shape, abcd, as shown in the figure, turns into a circular shape when placed in a region of magnetic field which is directed normal to the plane of the loop away from the reader. Predict the direction of the induced current in the wire.

Concept: Force on a Moving Charge in Uniform Magnetic and Electric Fields
Chapter: [3.02] Moving Charges and Magnetism
[1]2

Why must electrostatic field at the surface of a charged conductor be normal to the surface at every point? Give reason?

Concept: Electric Field Due to a Point Charge
Chapter: [1.02] Electric Charges and Fields
[1]3

Define one tesla using the expression for the magnetic force acting on a particle of charge q moving with velocity $\vec{v}$  in a magnetic field $\vec{B}$ .

Concept: Magnetic Force
Chapter: [3.02] Moving Charges and Magnetism
[1]4

In both β and β+ decay processes, the mass number of a nucleus remains the same, whereas the atomic number Z increases by one in β decay and decreases by one in β+ decay. Explain giving reason.

Concept: Atomic Spectra
Chapter: [8.02] Atoms
[1]5

Arrange the following electromagnetic waves in order of increasing frequency:
ϒ-rays, microwaves, infrared rays and ultraviolet rays.

Concept: Electromagnetic Waves
Chapter: [5.01] Electromagnetic Waves
[1]6

The figure shows the field lines on a positive charge. Is the work done by the field in moving a small positive charge from Q to P positive or negative? Give reason.

Concept: Electric Field Lines
Chapter: [1.02] Electric Charges and Fields
[1]7

In photoelectric effect, why should the photoelectric current increase as the intensity of monochromatic radiation incident on a photosensitive surface is increased? Explain.

Concept: Photoelectric Effect - Hertz’S Observations
Chapter: [7.01] Dual Nature of Radiation and Matter
[1]8

A ray of light falls on a transparent sphere with centre C as shown in the figure. The ray emerges from the sphere parallel to the line AB. Find the angle of refraction at A if the refractive index of the material of the sphere is $\sqrt{3}$.

Concept: The Parallel Plate Capacitor
Chapter: [1.01] Electrostatic Potential and Capacitance
[2]9

Two very small identical circular loops, (1) and (2), carrying equal currents I are placed vertically (with respect to the plane of the paper) with their geometrical axes perpendicular to each other as shown in the figure. Find the magnitude and direction of the net magnetic field produced at the point O.

Concept: Torque on a Current Loop in Magnetic Field
Chapter: [3.02] Moving Charges and Magnetism
[2]10

Show that the current leads the voltage in phase by π/2 in an AC circuit containing an ideal capacitor ?

Concept: Ac Voltage Applied to a Capacitor
Chapter: [4.01] Alternating Current
[2]11

Give two points to distinguish between a paramagnetic and a diamagnetic substance ?

Concept: Magnetisation and Magnetic Intensity
Chapter: [3.01] Magnetism and Matter
[2]12

Find the charge on the capacitor as shown in the circuit.

Concept: Energy Stored in a Capacitor
Chapter: [1.01] Electrostatic Potential and Capacitance
[2]13

Identify the equivalent gate represented by the circuit shown in the figure. Draw its logic symbol and write the truth table.

Concept: Integrated Circuits
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[2]14

Figure shows a ray of light passing through a prism. If the refracted ray QR is parallel to the base BC, show that (i) r1 = r2 = A/2 and (ii) angle of minimum deviation, Dm = 2i − A.

Concept: Dispersion by a Prism
Chapter: [6.01] Ray Optics and Optical Instruments
[2]15

Define the term modulation. Draw a block diagram of a simple modulator for obtaining AM signal ?

Concept: Modulation and Its Necessity
Chapter: [10.01] Communication Systems
[2]16
[1]16.1

How does oscillating charge produce electromagnetic waves?

Concept: Electromagnetic Waves
Chapter: [5.01] Electromagnetic Waves
[1]16.2

Sketch a schematic diagram depicting oscillating electric and magnetic fields of an em wave propagating along + z-direction ?

Concept: Motion in a Magnetic Field
Chapter: [3.02] Moving Charges and Magnetism
[2]17 | Attempt any one of the following.
[2]17.1

Draw energy band diagrams of an n-type and p-type semiconductor at temperature T > 0 K. Mark the donor and acceptor energy levels with their energies.

Concept: Energy Bands in Conductors, Semiconductors and Insulators
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[2]17.2

Distinguish between a metal and an insulator on the basis of energy band diagrams ?

Concept: Energy Bands in Conductors, Semiconductors and Insulators
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[2]18

In a series LCR circuit, obtain the condition under which the impedance of the circuit is minimum ?

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

In a series LCR circuit, obtain the condition under which watt-less current flows in the circuit ?

Concept: Ac Voltage Applied to a Series Lcr Circuit
Chapter: [4.01] Alternating Current
[3]19

The currents flowing in the two coils of self-inductance L1 = 16 mH and L2 = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of induced voltages ?

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

The currents flowing in the two coils of self-inductance L1 = 16 mH and L2 = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of  the currents ?

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

The currents flowing in the two coils of self-inductance L1 = 16 mH and L2 = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of the energies stored in the two coils at a given instant ?

Concept: Inductance - Self-Inductance
Chapter: [4.02] Electromagnetic Induction
[3]20
[1]20.1

A point charge (+Q) is kept in the vicinity of an uncharged conducting plate. Sketch the electric field lines between the charge and the plate?

Concept: Electric Field Lines
Chapter: [1.02] Electric Charges and Fields
[2]20.2

Two infinitely large plane thin parallel sheets having surface charge densities σ1 and σ2 (σ1 > σ2) are shown in the figure. Write the magnitudes and directions of the net fields in the regions marked II and III.

Concept: Force Between Two Parallel Currents, the Ampere
Chapter: [3.02] Moving Charges and Magnetism
[3]21
[1]21.1

Two long straight parallel conductors 'a' and 'b', carrying steady currents Ia and Ib are separated by a distance d. Write the magnitude and direction of the magnetic field produced by the conductor 'a' at the points along the conductor 'b'. If the currents are flowing in the same direction, what is the nature and magnitude of the force between the two conductors?

Concept: Force Between Two Parallel Currents, the Ampere
Chapter: [3.02] Moving Charges and Magnetism
[2]21.2

Show with the help of a diagram how the force between the two conductors would change when the currents in them flow in the opposite directions?

Concept: Motion in a Magnetic Field
Chapter: [3.02] Moving Charges and Magnetism
[3]22

Describe briefly, by drawing suitable diagram, the  sky wave ?

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

Describe briefly, by drawing suitable diagram, the space wave modes of propagation. Mention the frequency range of the waves in these modes of propagation ?

Concept: Propagation of Electromagnetic Waves
Chapter: [10.01] Communication Systems
[3]23
[2]23.1

Describe briefly how the Davisson-Germer experiment demonstrated the wave nature of electrons.

Concept: Wave Nature of Matter
Chapter: [7.01] Dual Nature of Radiation and Matter
[1]23.2

An electron is accelerated from rest through a potential V. Obtain the expression for the de-Broglie wavelength associated with it ?

Concept: de-Broglie Relation
Chapter: [7.01] Dual Nature of Radiation and Matter
[3]24

When Puja, a student of 10th class, watched her mother washing clothes in the open, she observed coloured soap bubbles and was curious to know why the soap bubbles appear coloured. In the evening when her father, an engineer by profession, came home, she asked him this question. Her father explained to her the basic phenomenon of physics due to which the soap bubbles appear coloured.
(a) What according to you are the values displayed by Puja and her father?
(b) State the phenomenon of light involved in the formation of coloured soap bubbles.

Concept: Electromagnetic Induction
Chapter: [4.02] Electromagnetic Induction
[3]25 | Attempt any on of the following.
[3]25.1
[1]25.1.1

Why is zener diode fabricated by heavily doping both p- and n-sides of the junction?

Concept: Special Purpose P-n Junction Diodes
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[2]25.1.2

Draw the circuit diagram of zener diode as a voltage regulator and briefly explains its working ?

Concept: Zener Diode as a Voltage Regulator
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[3]25.2
[1]25.2.1

How is a photodiode fabricated?

Concept: Special Purpose P-n Junction Diodes
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[2]25.2.2

Briefly explain its working. Draw its V - I characteristics for two different intensities of illumination ?

Concept: Special Purpose P-n Junction Diodes
Chapter: [9.01] Semiconductor Electronics - Materials, Devices and Simple Circuits
[3]26
[1]26.1

Distinguish between unpolarised and linearly polarised light.

Concept: Plane Polarised Light
Chapter: [6.02] Wave Optics
[1]26.2

What dose a polaroid consist of?

Concept: Polarisation
Chapter: [6.02] Wave Optics

What does a polaroid consist of? How does it produce a linearly polarised light?

Concept: Polarisation
Chapter: [6.02] Wave Optics
[1]26.3

Explain briefly how sunlight is polarised by scattering through atmospheric particles.

Concept: Plane Polarised Light
Chapter: [6.02] Wave Optics
[3]27

In a parallel plate capacitor with air between the plates, each plate has an area of 6 × 10−3 m2 and the separation between the plates is 3 mm.
(i) Calculate the capacitance of the capacitor.
(ii) If this capacitor is connected to 100 V supply, what would be the charge on each plate?
(iii) How would charge on the plates be affected, if a 3 mm thick mica sheet of K = 6 is inserted between the plates while the voltage supply remains connected?

Concept: The Parallel Plate Capacitor
Chapter: [1.01] Electrostatic Potential and Capacitance
[5]28 | Attempt any one of the following.
[5]28.1
[3]28.1.1

Using Bohr's postulates, derive the expression for the total energy of the electron in the stationary states of the hydrogen atom ?

Concept: Bohr'S Model for Hydrogen Atom
Chapter: [8.02] Atoms
[2]28.1.2

Using Rydberg formula, calculate the wavelengths of the spectral lines of the first member of the Lyman series and of the Balmer series.

Concept: Hydrogen Spectrum
Chapter: [8.02] Atoms
[5]28.2
[3]28.2.1

Define the terms (i) half-life (T1/2) and (ii) average life (τ). Find out their relationships with the decay constant (λ).

Concept: Mass-energy and Nuclear Binding Energy - Nuclear Binding Energy
Chapter: [8.01] Nuclei
[2]28.2.2

A radioactive nucleus has a decay constant λ = 0.3465 (day)–1. How long would it take the nucleus to decay to 75% of its initial amount?

Chapter: [8.01] Nuclei
[5]29 | Attempt any one of the following.
[5]29.1
[2]29.1.1

State the principle of a potentiometer. Define potential gradient. Obtain an expression for potential gradient in terms of resistivity of the potentiometer wire.

Concept: Potentiometer
Chapter: [2.01] Current Electricity
[3]29.1.2

Figure shows a long potentiometer wire AB having a constant potential gradient. The null points for the two primary cells of emfs ε1 and ε2 connected in the manner shown are obtained at a distance of l1 = 120 cm and l2 = 300 cm from the end A. Determine (i) ε12 and (ii) position of null point for the cell ε1 only.

Concept: Potentiometer
Chapter: [2.01] Current Electricity
[5]29.2
[3]29.2.1

Define the term 'drift velocity' of charge carriers in a conductor. Obtain the expression for the current density in terms of relaxation time ?

Concept: Electric Current
Chapter: [2.01] Current Electricity
[2]29.2.2

A 100 V battery is connected to the electric network as shown. If the power consumed in the 2 Ω resistor is 200 W, determine the power dissipated in the 5 Ω resistor.

Concept: Electric Current
Chapter: [2.01] Current Electricity
[5]30 | Attempt any one of the following.
[5]30.1
[3]30.1.1

Draw a labelled ray diagram of an astronomical telescope to show the image formation of a distant object. Write the main considerations required in selecting the objective and eyepiece lenses in order to have large magnifying power and high resolution of the telescope.

Concept: Optical Instruments - Telescope
Chapter: [6.01] Ray Optics and Optical Instruments
[2]30.1.2

A compound microscope has an objective of focal length 1.25 cm and eyepiece of focal length 5 cm. A small object is kept at 2.5 cm from the objective. If the final image formed is at infinity, find the distance between the objective and the eyepiece ?

Concept: Optical Instruments - The Microscope
Chapter: [6.01] Ray Optics and Optical Instruments
[5]30.2
[3]30.2.1

Write three characteristic features to distinguish between the interference fringes in Young's double slit experiment and the diffraction pattern obtained due to a narrow single slit.

Concept: Interference of Light Waves and Young’S Experiment
Chapter: [6.02] Wave Optics
[2]30.2.2

A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is at a distance of 2.5 mm from the centre of the screen. Find the width of the slit.

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

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