Science (English Medium) Class 12 - CBSE Question Bank Solutions

A device X used in communication system can convert one form of energy into another. Name the device X. Explain the function of a repeater in a communication system.

Distinguish between point to point and broadcast modes of communication. Give an example of each.

Explain the basic concept of mobile telephoning ?

Distinguish between point to point and broadcast modes of communication. Give an example of each.

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

Do the emitted photoelectrons have the same kinetic energy?

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

Does the kinetic energy of the emitted electrons depend on the intensity of incident radiation?

A beam of monochromatic radiation is incident on a photosensitive surface. Answer the following question giving reason :

On what factors does the number of emitted photoelectrons depend?

A plane wavefront propagating in a medium of refractive index 'μ₁' is incident on a plane surface making the angle of incidence 'i' as shown in the figure. It enters into a medium of refractive index 'μ₂' (μ₂ > μ₁). Use Huygens' construction of secondary wavelets to trace the propagation of the refracted wavefront. Hence verify Snell's law of refraction.

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.

In the circuit shown in the figure, find the total resistance of the circuit and the current in the arm AD.

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

 In a typical nuclear reaction, e.g.

`"_1^2H+"_1^2H ->"_2^3He + n + 3.27 \text { MeV },`

although number of nucleons is conserved, yet energy is released. How? Explain.

Figure shows a rectangular loop conducting PQRS in which the arm PQ is free to move. A uniform magnetic field acts in the direction perpendicular to the plane of the loop. Arm PQ is moved with a velocity v towards the arm Rs. Assuming that the arms QR, RS and SP have negligible resistances and the moving arm PQ has the resistance r, obtain the expression for (i) the current in the loop (ii) the force and (iii) the power required to move the arm PQ.

How does the mutual inductance of a pair of coils change when

(i) distance between the coils is increased and

(ii) number of turns in the coils is increased?

Draw the plot of binding energy per nucleon (BE/A) as a functino of mass number A. Write two important conclusions that can be drawn regarding the nature of nuclear force.

An electric dipole is held in a uniform electric field.

(i) Show that the net force acting on it is zero.

(ii) The dipole is aligned parallel to the field. Find the work done in rotating it through the angle of 180°.

Write the relationship between the size of a nucleus and its mass number (A)?

State Gauss’s law in electrostatics. A cube which each side ‘a’ is kept is an electric field given by `vecE` = C × l. (as is shown in the figure where C is a positive dimensional constant. Find out

(i) The electric flux through the cube, and

(ii) The net charge inside the cube.

Using the curve for the binding energy per nucleon as a function of mass number A, state clearly how the release in energy in the processes of nuclear fission and nuclear fusion can be explained.

Draw a plot showing the variation of photoelectric current with collector plate potential for two different frequencies, v₁ > v₂, of incident radiation having the same intensity. In which case will the stopping potential be higher? Justify your answer.