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

How does the resistivity of a semiconductor change with rise of temperature ? Explain.

Draw the pattern of electric field lines, when a point charge –Q is kept near an uncharged conducting plate.

Answer the following question.
State Bohr's quantization condition of angular momentum. Calculate the shortest wavelength of the Bracket series and state to which part of the electromagnetic spectrum it belongs. 

Plot a graph showing the variation of de Broglie wavelength (X) associated with a charged a particle of mass m, versus  `1/sqrtV` where V is the potential difference through which the particle is accelerated. How does this graph give us information regarding the magnitude of the charge of the particle? 

Answer the following question.
Why photodiodes are required to operate in reverse bias? Explain.

Answer the following question.
Draw the pattern of electric field lines when a point charge +q is kept near an uncharged conducting plate.

Answer the following question.
Derive an expression for the electric field due to a dipole of dipole moment `vec"p"` at a point on its perpendicular bisector.

Use Einstein's photoelectric equation to show how from this graph,
(i) Threshold frequency, and
(ii) Planck's constant can be determined.

In Young's double-slit experiment, the two slits are separated by a distance of 1.5 mm, and the screen is placed 1 m away from the plane of the slits. A beam of light consisting of two wavelengths of 650 nm and 520 nm is used to obtain interference fringes.
Find the distance of the third bright fringe for λ = 520 nm on the screen from the central maximum.

Choose the correct answer from given options
Photons of frequency v are incident on the surface of two metals A and B of threshold frequency 3/4 v and 2/3 v, respectively. The ratio of maximum kinetic energy of electrons emitted from A to that from B is

Write the conditions on path difference under which constructive interference occurs in Young’s double-slit experiment.

Explain why two field lines never cross each other at any point?

Choose the correct alternative:

Alloys usually have much (lower/higher) temperature coefficients of resistance than pure metals.

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The resistivity of the alloy manganin is nearly independent of/increases rapidly with increase of temperature.

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The resistivity of a typical insulator (e.g., amber) is greater than that of a metal by a factor of the order of (10²²/10²³).

A sample of paramagnetic salt contains 2.0 × 10²⁴ atomic dipoles each of dipole moment 1.5 × 10^–23 J T^–1. The sample is placed under a homogeneous magnetic field of 0.64 T, and cooled to a temperature of 4.2 K. The degree of magnetic saturation achieved is equal to 15%. What is the total dipole moment of the sample for a magnetic field of 0.98 T and a temperature of 2.8 K? (Assume Curie’s law)

If a charge q₀ is there in an electric field caused by several point charges q_i. The potential energy of q₀ is given by ________.

Which of these equations is the correct expression for force on a charge in magnetic field?

The magnitude of the magnetic field due to a circular coil of radius R carrying a current I at an axial distance x from the centre is ______.

The magnetic field at a distance r from a long wire carrying current I is 0.4 tesla. The magnetic field at a distance 2 r is ______.