Science (English Medium) इयत्ता १२ - CBSE Important Questions for Physics

Explain the formation of the barrier potential in a p-n junction.

Pieces of copper and of silicon are initially at room temperature. Both are heated to temperature T. The conductivity of ______.

Answer the following giving reasons:

A p-n junction diode is damaged by a strong current.

Answer the following giving reasons:

Impurities are added to intrinsic semiconductors.

During the formation of a p-n junction ______.

Explain the terms Attenuation used in Communication System.

Explain any two factors that justify the need of modulating a low-frequency signal.

How is amplitude modulation achieved?

The frequencies of two side bands in an AM wave are 640 kHz and 660 kHz respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation?

Write two advantages of frequency modulation over amplitude modulation.

Define the term modulation. Draw a block diagram of a simple modulator for obtaining AM signal ?

Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.

In the given block diagram of a receiver, identify the boxes labeled as X and Y and write their functions.

Given modulation index physical significance .For an amplitude modulated wave, the maximum amplitude is found to be 10 V while the minimum amplitude is 2 V. Determine the modulation index μ ?

What do you mean by bandwidth of a signal? Give its importance. 

Differentiate between Analog and Digital communication. 

Answer the following question.
Why a signal transmitted from a TV tower cannot be received beyond a certain distance? Write the expression for the optimum separation between the receiving and the transmitting antenna.

Answer the following question.
If A and B represent the maximum and minimum amplitudes of an amplitude-modulated wave, write the expression for the modulation index in terms of A and B.

Solve the following question.
A message signal of frequency 20 kHz and peak voltage 10 V is used to modulate a carrier of frequency 2 MHz and peak voltage of 15 V. Calculate the modulation index. Why the modulation index is generally kept less than one? 

What is the amount of work done in moving a point charge Q around a circular arc of radius ‘r’ at the centre of which another point charge ‘q’ is located?