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

Write the functions of the following in communication systems:

Receiver

Write the functions of the following in communication systems:

Demodulator

Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

Two charges 5 × 10⁻⁸ C and −3 × 10⁻⁸ C are located 16 cm apart. At what point(s) on the line joining the two charges is the electric potential zero? Take the potential at infinity to be zero.

Is Ohm’s law universally applicable for all conducting elements? If not, give examples of elements which do not obey Ohm’s law.

A low voltage supply from which one needs high currents must have very low internal resistance. Why?

A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20 A in 0.5 s, what is the change of flux linkage with the other coil?

The refractive index of glass is 1.5. What is the speed of light in glass? (Speed of light in vacuum is 3.0 × 10⁸ m s⁻¹)

Is the speed of light in glass independent of the colour of light? If not, which of the two colours red and violet travels slower in a glass prism?

Explain how Corpuscular theory predicts the speed of light in a medium, say, water, to be greater than the speed of light in vacuum. Is the prediction confirmed by experimental determination of the speed of light in water? If not, which alternative picture of light is consistent with the experiment?

Let us list some of the factors, which could possibly influence the speed of wave propagation:

(i) Nature of the source

(ii) Direction of propagation

(iii) Motion of the source and/or observer

(iv) Wavelength

(v) Intensity of the wave

On which of these factors, if any, does the speed of light in vacuum?

What is the shortest wavelength present in the Paschen series of spectral lines?

Asha's mother read an article in the newspaper about a disaster that took place at Chernobyl. She could not understand much from the articles and asked a few questions from Asha regarding the article. Asha tried to answer her mother's questions based on what she learnt in Class XII Physics.

(a) What was the installation at Chernobyl where the disaster took place? What according to you, was the cause of this disaster?

(b) Explain the process of release of energy in the installation at Chernobyl.

(c) What according to you, were the values displayed by Asha and her mother?

Explain the term demodulation used in a communication system.

A photosensitive surface emits photoelectrons when red light falls on it. Will the surface emit photoelectrons when blue light is incident on it? Give reason. 

Distinguish between broadcast mode and point-to-point mode of communication and give one example for each.

Draw a plot showing the variation of photoelectric current with collector potential for different frequencies but same intensity of incident radiation ?

Use Einstein's photoelectric equation to explain the observations from this graph ?

What change will you observe if intensity of incident radiation is changed but the frequency remains the same?

An electron jumps from fourth to first orbit in an atom. How many maximum number of spectral lines can be emitted by the atom? To which series these lines correspond?