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

Using Huygens's construction of secondary wavelets explain how a diffraction pattern is obtained on a screen due to a narrow slit on which a monochromatic beam of light is incident normally.

Using Rutherford's model of the atom, derive the expression for the total energy of the electron in hydrogen atom. What is the significance of total negative energy possessed by the electron?

Figure shows a capacitor made of two circular plates each of radius 12 cm, and separated by 5.0 cm. The capacitor is being charged by an external source (not shown in the figure). The charging current is constant and equal to 0.15 A.

1. Calculate the capacitance and the rate of charge of the potential difference between the plates.
2. Obtain the displacement current across the plates.
3. Is Kirchhoff’s first rule (junction rule) valid at each plate of the capacitor? Explain.

A parallel plate capacitor (Figure) made of circular plates each of radius R = 6.0 cm has a capacitance C = 100 pF. The capacitor is connected to a 230 V ac supply with a (angular) frequency of 300 rad s⁻¹.

1. What is the rms value of the conduction current?
2. Is the conduction current equal to the displacement current?
3. Determine the amplitude of B at a point 3.0 cm from the axis between the plates.

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 ______.