Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions for Physics

A small candle, 2.5 cm in size is placed at 27 cm in front of a concave mirror of radius of curvature 36 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image. If the candle is moved closer to the mirror, how would the screen have to be moved?

A 4.5 cm needle is placed 12 cm away from a convex mirror of focal length 15 cm. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

What is the shape of the wavefront in the following case?

Light diverging from a point source.

What is the shape of the wavefront in the following case?

Light emerging out of a convex lens when a point source is placed at its focus.

What is the shape of the wavefront in the following case?

The portion of the wavefront of light from a distant star was intercepted by the Earth.

You have learnt in the text how Huygens’ principle leads to the laws of reflection and refraction. Use the same principle to deduce directly that a point object placed in front of a plane mirror produces a virtual image whose distance from the mirror is equal to the object distance from the mirror.

Find the maximum frequency of X-rays produced by 30 kV electrons.

Find the (a) maximum frequency and (b) minimum wavelength of X-rays produced by 30 kV electrons.

The work function of caesium metal is 2.14 eV. When light of frequency 6 × 10¹⁴ Hz is incident on the metal surface, photoemission of electrons occurs. What is the

1. maximum kinetic energy of the emitted electrons,
2. Stopping potential, and
3. maximum speed of the emitted photoelectrons?

Quarks inside protons and neutrons are thought to carry fractional charges [(+2/3)e; (–1/3)e]. Why do they not show up in Millikan’s oil-drop experiment?

Why should gases be insulators at ordinary pressures and start conducting at very low pressures?

The size of the atom in Thomson’s model is ______ the atomic size in Rutherford’s model.

In the ground state of ______ electrons are in stable equilibrium, while in ______ electrons always experience a net force.

A classical atom based on ______ is doomed to collapse.

An atom has a nearly continuous mass distribution in a ______ but has a highly non-uniform mass distribution in ______.

The positively charged part of the atom possesses most of the mass in ______.

Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K.) What results do you expect?

Answer the following question, which help you understand the difference between Thomson’s model and Rutherford’s model better.

Is the average angle of deflection of α­-particles by a thin gold foil predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?

Answer the following question, which help you understand the difference between Thomson’s model and Rutherford’s model better.

Is the probability of backward scattering (i.e., scattering of α-particles at angles greater than 90°) predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?

Answer the following question, which help you understand the difference between Thomson’s model and Rutherford’s model better.

Keeping other factors fixed, it is found experimentally that for small thickness t, the number of α-particles scattered at moderate angles is proportional to t. What clue does this linear dependence on t provide?