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

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?

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

In which model is it completely wrong to ignore multiple scattering for the calculation of average angle of scattering of α-particles by a thin foil?

From the relation R = R₀A¹/³, where R₀ is a constant and A is the mass number of a nucleus, show that the nuclear matter density is nearly constant (i.e. independent of A).

In an n-type silicon, which of the following statement is true:

A double convex lens is made of a glass of refractive index 1.55, with both faces of the same radius of curvature. Find the radius of curvature required, if the focal length is 20 cm.

State Huygen’s principle.

Consider a plane wave front incident on a thin convex lens. Draw a proper diagram to show how the incident wave front traverses through the lens and after refraction focusses on the focal point of the lens, giving the shape of the emergent wave front.

Use Huygens' principle to verify the laws of refraction.