Date: March 2014

Define the term 'electrical conductivity' of a metallic wire. Write its S.I. unit.

Chapter: [0.03] Current Electricity

The carrier wave is represented by

Chapter: [0.15] Communication Systems

Show variation of resistivity of Si with temperature in a graph ?

Chapter: [0.03] Current Electricity

A convex lens is placed in contact with a plane mirror. A point object at a distance of 20 cm on the axis of this combination has its image coinciding with itself. What is the focal length of the lens?

Chapter: [0.09] Ray Optics and Optical Instruments

"For any charge configuration, equipotential surface through a point is normal to the electric field." Justify.

Chapter: [0.02] Electric Charges and Fields

Write the expression, in a vector form, for the Lorentz magnetic force \[\vec{F}\] due to a charge moving with velocity \[\vec{V}\] in a magnetic field \[\vec{B}\]. What is the direction of the magnetic force?

Chapter: [0.05] Moving Charges and Magnetism

The figure given below shows the block diagram of a generalized communication system. Identify the element labelled 'X' and write its function.

Chapter: [0.15] Communication Systems

Two spherical bobs, one metallic and the other of glass, of the same size are allowed to fall freely from the same height above the ground. Which of the two would reach earlier and why?

Chapter: [0.07] Electromagnetic Induction

A capacitor 'C', a variable resistor 'R' and a bulb 'B' are connected in series to the ac mains in circuit as shown. The bulb glows with some brightness. How will the glow of the bulb change if (i) a dielectric slab is introduced between the plates of the capacitor, keeping resistance R to be the same; (ii) the resistance R is increased keeping the same capacitance?

Chapter: [0.01] Electrostatic Potential and Capacitance

An electric dipole of length 2 cm, when placed with its axis making an angle of 60° with a uniform electric field, experiences a torque of \[8\sqrt{3}\] Nm. Calculate the potential energy of the dipole, if it has a charge \[\pm\] 4 nC.

Chapter: [0.02] Electric Charges and Fields

Out of the two magnetic materials, 'A' has relative permeability slightly greater than unity while 'B' has less than unity. Identify the nature of the materials 'A' and 'B'. Will their susceptibilities be positive or negative?

Chapter: [0.04] Magnetism and Matter

State the underlying principle of a cyclotron. Write briefly how this machine is used to accelerate charged particles to high energies

Chapter: [0.05] Moving Charges and Magnetism

For a single slit of width "a", the first minimum of the interference pattern of a monochromatic light of wavelength λ occurs at an angle of λa. At the same angle of λa, we get a maximum for two narrow slits separated by a distance "a". Explain.

Chapter: [0.1] Wave Optics

Write the truth table for the combination of the gates shown. Name the gates used.

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

Identify the logic gates marked 'P' and 'Q' in the given circuit. Write the truth table for the combination.

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

A proton and an alpha particle are accelerated through the same potential. Which one of the two has (i) greater value of de−Broglie wavelength associated with it and (ii) less kinetic energy. Give reasons to justify your answer.

Chapter: [0.11] Dual Nature of Radiation and Matter

Given a uniform electric field \[\vec{E} = 2 \times {10}^3 \ \hat{i}\] N/C, find the flux of this field through a square of side 20 cm, whose plane is parallel to the y−z plane. What would be the flux through the same square, if the plane makes an angle of 30° with the x−axis ?

Chapter: [0.02] Electric Charges and Fields

State the two Kirchhoff’s rules used in electric networks. How are there rules justified?

Chapter: [0.03] Current Electricity

Monochromatic light of frequency 6.0 × 10^{14} Hz is produced by a laser. The power emitted is 2.0 × 10^{−3} W. Estimate the number of photons emitted per second on an average by the source

Chapter: [0.1] Wave Optics

Draw a plot showing the variation of photoelectric current versus the intensity of incident radiation on a given photosensitive surface.

Chapter: [0.11] Dual Nature of Radiation and Matter

State Ampere’s circuital law

Chapter: [0.05] Moving Charges and Magnetism

Two long coaxial insulated solenoids, S_{1} and S_{2} of equal lengths are wound one over the other as shown in the figure. A steady current "I" flow thought the inner solenoid S_{1} to the other end B, which is connected to the outer solenoid S_{2} through which the same current "I" flows in the opposite direction so as to come out at end A. If n_{1} and n_{2} are the number of turns per unit length, find the magnitude and direction of the net magnetic field at a point (i) inside on the axis and (ii) outside the combined system

Chapter: [0.05] Moving Charges and Magnetism

A 12.9 eV beam of electronic is used to bombard gaseous hydrogen at room temperature. Upto which energy level the hydrogen atoms would be excited ?

Calculate the wavelength of the first member of Paschen series and first member of Balmer series.

Chapter: [0.13] Atoms

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

Chapter: [0.09] Ray Optics and Optical Instruments

The total magnification produced by a compound microscope is 20. The magnification produced by the eye piece is 5. The microscope is focussed on a certain object. The distance between the objective and eyepiece is observed to be 14 cm. If least distance of distinct vision is 20 cm, calculate the focal length of the objective and the eye piece.

Chapter: [0.09] Ray Optics and Optical Instruments

Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range ?

Chapter: [0.08] Electromagnetic Waves

The small ozone layer on top of the stratosphere is crucial for human survival. Why?

Chapter: [0.08] Electromagnetic Waves

Why is the amount of the momentum transferred by the em waves incident on the surface so small ?

Chapter: [0.08] Electromagnetic Waves

When Sunita, a class XII student, came to know that her parents are planning to rent out the top floor of their house to a mobile company she protested. She tried hard to convince her parents that this move would be a health hazard.

Ultimately her parents agreed :

(1) In what way can the setting up of transmission tower by a mobile company in a residential colony prove to be injurious to health?

(2) By objecting to this move of her parents, what value did Sunita display?

(3) Estimate the range of e.m. waves which can be transmitted by an antenna of height 20 m. (Given radius of the earth = 6400 km)

Chapter: [0.08] Electromagnetic Waves

A potentiometer wire of length 1.0 m has a resistance of 15 Ω. It is connected to a 5 V battery in series with a resistance of 5 Ω. Determine the emf of the primary cell which gives a balance point at 60 cm.

Chapter: [0.03] Current Electricity

Derive the mathematical expression for law of radioactive decay for a sample of a radioactive nucleus

Chapter: [0.12] Nuclei

Write symbolically the process expressing the β^{+} decay of `""_11^22Na`. Also write the basic nuclear process underlying this decay.

Chapter: [0.12] Nuclei

Is the nucleus formed in the decay of the nucleus `""_11^22Na`, an isotope or isobar?

Chapter: [0.12] Nuclei

A mobile phone lies along the principal axis of a concave mirror. Show, with the help of a suitable diagram, the formation of its image. Explain why magnification is not uniform.

Chapter: [0.09] Ray Optics and Optical Instruments

Suppose the lower half of the concave mirror's reflecting surface is covered with an opaque material. What effect this will have on the image of the object? Explain

Chapter: [0.09] Ray Optics and Optical Instruments

Obtain the expression for the energy stored per unit volume in a charged parallel plate capacitor.

Chapter: [0.01] Electrostatic Potential and Capacitance

The electric field inside a parallel plate capacitor is E. Find the amount of work done in moving a charge q over a closed loop a b c d a.

Chapter: [0.01] Electrostatic Potential and Capacitance

Derive the expression for the capacitance of a parallel plate capacitor having plate area A and plate separation d.

Chapter: [0.01] Electrostatic Potential and Capacitance

Two charged spherical conductors of radii R_{1} and R_{2} when connected by a conducting wire acquire charges q_{1} and q_{2} respectively. Find the ratio of their surface charge densities in terms of their radii.

Chapter: [0.01] Electrostatic Potential and Capacitance

Describe a simple experiment (or activity) to show that the polarity of emf induced in a coil is always such that it tends to produce a current which opposes the change of magnetic flux that produces it.

Chapter: [0.07] Electromagnetic Induction

The current flowing through an inductor of self inductance L is continuously increasing. Plot a graph showing the variation of

Magnetic flux versus the current

Chapter: [0.07] Electromagnetic Induction

The current flowing through an inductor of self-inductance L is continuously increasing. Plot a graph showing the variation of

Induced emf versus dI/dt

Chapter: [0.07] Electromagnetic Induction

The current flowing through an inductor of self inductance L is continuously increasing. Plot a graph showing the variation of Magnetic potential energy stored versus the current.

Chapter: [0.07] Electromagnetic Induction

Draw a schematic sketch of an ac generator describing its basic elements. State briefly its working principle. Show a plot of variation of

(i) Magnetic flux and

(ii) Alternating emf versus time generated by a loop of wire rotating in a magnetic field.

Chapter: [0.07] Electromagnetic Induction

Why is choke coil needed in the use of fluorescent tubes with ac mains?

Chapter: [0.06] Alternating Current

Explain with the help of a diagram, how depletion region and potential barrier are formed in a junction diode.

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Reverse biasing

How are these characteristics made use of in rectification?

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

Using the necessary circuit diagrams, show how the V-I characteristics of a p-n junction are obtained in

Forward biasing

How are these characteristics made use of in rectification?

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

Differentiate between three segments of a transistor on the basis of their size and level of doping.

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

How is a transistor biased to be in active state?

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

With the help of necessary circuit diagram, describe briefly how n-p-n transistor in CE configuration amplifies a small sinusoidal input voltage. Write the expression for the ac current gain

Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits

'Two independent monochromatic sources of light cannot produce a sustained interference pattern'. Give reason.

Chapter: [0.1] Wave Optics

Light waves each of amplitude "a" and frequency "ω", emanating from two coherent light sources superpose at a point. If the displacements due to these waves are given by y_{1} = a cos ωt and y_{2} = a cos(ωt + ϕ) where ϕ is the phase difference between the two, obtain the expression for the resultant intensity at the point.

Chapter: [0.1] Wave Optics

In Young's double slit experiment, using monochromatic light of wavelength λ, the intensity of light at a point on the screen where path difference is λ, is K units. Find out the intensity of light at a point where path difference is λ/3.

Chapter: [0.1] Wave Optics

How does one demonstrate, using a suitable diagram, that unpolarised light when passed through a Polaroid gets polarised?

Chapter: [0.1] Wave Optics

A beam of unpolarised light is incident on a glass-air interface. Show, using a suitable ray diagram, that light reflected from the interface is totally polarised, when μ = tan i_{B}, where μ is the refractive index of glass with respect to air and i_{B} is the Brewster's angle.

Chapter: [0.1] Wave Optics

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