Science (English Medium) कक्षा १२ - CBSE Important Questions

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? 

Describe any four consequences of the disintegration of Soviet Union

American involvement in South Asia has rapidly increased after the Cold War. Give two examples to illustrate.

Identify the group of countries that had been part of the Soviet Union before its disintegration.

What is the full form of “SAARC”?

Why did the superpowers need smaller states as their allies? Explain any four reasons.

Analyse India’s changing relationship with post-Communist Russia.

Analyse any three happenings during Gorbachev's period that led to the disintegration of the Soviet Union.

Study the cartoon given below carefully and answer the following questions:

i. The given cartoon is related to which country?

ii. Which two symbols in this cartoon helped in identifying the country?

iii. What message does this cartoon convey to the world?

Assess the role of ASEAN as an economic association.

What makes the European Union a highly influential regional organisation?

Explain the term 'ASEAN WAY'.

Explain any two major policy decisions made by the Chinese government to open and develop its economy.