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

Draw the sketches to differentiate between plane wavefront and spherical wavefront.

Monochromatic light of wavelength 589 nm is incident from air on a water surface. What are the wavelength, frequency and speed of (a) reflected and (b) refracted light? Refractive index of water is 1.33.

Define a wavefront.

Is the colour of 620 nm light and 780 nm light same? Is the colour of 620 nm light and 621 nm light same? How many colours are there in white light?

The wavelength of light in a medium is \[\lambda = \lambda_0 /\mu,\] where \[\lambda \] is the wavelength in vacuum. A beam of red light \[\left( \lambda_0 = 720\text{ nm} \right)\] enters water. The wavelength in water is \[\lambda =  \lambda_0 /\mu = 540\text{ nm.}\] To a person under water, does this light appear green?

If we put a cardboard (say 20 cm × 20 cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and out ear, we hear the sound almost clearly. Explain.

TV signals broadcast by a Delhi studio cannot be directly received at Patna, which is about 1000 km away. But the same signal goes some 36000 km away to a satellite, gets reflected and is then received at Patna. Explain.

Is it necessary to have two waves of equal intensity to study interference pattern? Will there be an effect on clarity if the waves have unequal intensity?

Light is _______________ .

The speed of light depends ____________ .

The equation of a light wave is written as \[y = A \sin\left( kx - \omega t \right).\] Here, `y` represents _______ .

An amplitude modulated (AM) radio wave bends appreciably round the corners of a 1 m × 1 m board but a frequency modulated (FM) wave only bends negligibly. If the average wavelengths of the AM and FM waves are \[\lambda_a   and   \lambda_f,\]

The inverse square law of intensity \[\left(\text{i.e. the intensity }\infty \frac{1}{r^2}\right)\] is valid for a ____________ .

A light wave can travel

(a) in vacuum

(b) in vacuum only

(c) in a material medium

(d) in a material medium only

Which of the following properties of light conclusively support the wave theory of light?

(a) Light obeys the laws of reflection.

(b) Speed of light in water is smaller than its speed in vacuum.

(c) Light shows interference.

(d) Light shows photoelectric effect.

When light propagates in vacuum, there is an electric field as well as a magnetic field. These fields ____________ .

(a) are constant in time

(b) have zero average value

(c) are perpendicular to the direction of propagation of light.

(d) are mutually perpendicular

Three observers A, B and C measure the speed of light coming from a source to be ν_A, ν_Band ν_C. A moves towards the source and C moves away from the source at the same speed. B remains stationary. The surrounding space is vacuum everywhere.

(a) \[\nu_A  >  \nu_B  >  \nu_C\]

(b) \[\nu_A  <  \nu_B  <  \nu_C\]

(c) \[\nu_A  =  \nu_B  =  \nu_C\]

(d) \[\nu_B  = \frac{1}{2}\left( \nu_A + \nu_C \right)\]

Three observers A, B and C measure the speed of light coming from a source to be ν_A, ν_Band ν_C. A moves towards the source and C moves away from the source at the same speed. B remains stationary. The surrounding space is water everywhere.

(a) \[\nu_A  >  \nu_B  >  \nu_C\]

(b) \[\nu_A  <  \nu_B  <  \nu_C\]

(c) \[\nu_A  =  \nu_B  =  \nu_C\]

(d) \[\nu_B  = \frac{1}{2}\left( \nu_A + \nu_C \right)\]

Find the range of frequency of light that is visible to an average human being

\[\left( 400\text{ nm }< \lambda < 700\text{ nm}\right)\]

The wavelength of sodium light in air is 589 nm. (a) Find its frequency in air. (b) Find its wavelength in water (refractive index = 1.33). (c) Find its frequency in water. (d) Find its speed in water.