Download SEMI CONDUCTOR AND COMMUNICATION

a)
b)
c)
d)
NAVODAYA VIDYALAYA SAMITHI
Hyderabad Region
PHYSICS
SAMPLE PAPER 5
Max. Marks: 70
CLASS XII
Topics:
1. Electronic devices
2. communication systems
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INSTRUCTIONS:
Question no 1 to 8 are very short answer questions and each carry 1mark.
Question no 9 to16 are short answer questions and each carry 2marks.
Question no 17 to 25 are short answer questions and each carry 3marks.
Question no 26 is value based question and carry 4marks.
e) Question no 27 to 29 are long answer questions and each carry 5mark.
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1. Which one of the two Diodes D1 and D2 in the given figures (i) Forward Biased and
(ii) Reverse Biased?
2. Name one impurity each, which when added to pure Germanium produces
(i) n- type
and p- type semi Conductor.
3. The current gain of a transistor in common base mode is 0.98. What is the current gain of
the transistor when it is used in a common emitter mode?
4. What kinds of biasing are required to collector and base of a transistor in common emitter
amplifier?
5. Give the logic symbol of AND gate and write its truth table.
6. Write the truth table for the following combination of gates.
7. Give the reason why microwaves are best suited for long distance transmission
8. What is the purpose of modulating a signal in transmission?
9. Distinguish
between
intrinsic
and
extrinsic
semiconductors?
or
Distinguish between conductors, insulators, and semi conductors based on energy band
diagrams?
10. Germanium and silicon junctions diodes are connected in parallel and the combination is
connected in series with a resistance R, a milliammeter (mA) and a key K as shown in fig.
When key is closed, a current begins to flow in the milliammeter. What will be the maximum
reading
of
the
voltmeter
connected
across
R?
11. For a CE amplifier, the audio signal voltage across the collector resistance of 2kΩ 2V.
Suppose the current amplification factor of the transistor is 100, find the input signal voltage
and base current, if the base resistance is 1kΩ.
12. Draw and explain the output waveform when the given inputs A and B are fed to a two input
OR gate.
13. What is sky wave communication? Why this mode of communication is restricted only to the
frequencies up to a few mega hertz?
14. A T V tower has a height of 400m at a given place. Calculate its coverage range if the radius
of the earth is 6400km.
15. Draw a labeled diagram of a simple modulator for obtaining an AM signal
16. In the given block diagram of a receiver, identify the boxes labeled as X and Y and write their
function.
17. With the help of a circuit diagram and working principle, explain the working of a Full wave
rectifier and also draw Input and output waveforms.
18. (a) Why is a Photo Diode is operated in reverse bias mode?
(b) For what purpose a photodiode is used?
(c) Draw its I – V characteristics for different intensities of illumination.
19. A transistor has a current amplification factor of 50. In a Common Emitter amplifier circuit,
the collector resistance is chosen as 5kΩ and the input resistance is 1kΩ. Calculate the
output
voltage
if
the
input
voltage
is
0.01V
OR
Explain the terms Current Gain, Power Gain, and Trans Conductance of a Transistor in
common emitter amplifier.
20. The above gate is known as XOR gate. Identify the gates P, Q and R from the above figure
and write Truth Table.
21. Derive an expression for height of a T. V. tower for transmission of signals for a given
coverage range. By what percent will the transmission range of a T V tower be affected when
the height of the tower is increased by 21%.
22. Explain the terms Ground Wave, Sky wave and Space wave.
23. Write the differences between AM and FM and also draw both signal waveforms. Why FM is
more advantageous than AM?
24. Differentiate between PAM, PDM, PCM used for multi channel communication.
25. Explain the terms Carrier Wave, Band width and Transducer.
26. Mahesh used to live with his grand father. Mahesh’s grand father asked him to purchase a
torch because the old one was not working. Mahesh made a torch by using LED and gave it
to his grand father as a gift and by explained why this torch is more advantageous then the
old one which uses a bulb. His grand father was very happy
a. What conclusion do you draw from the incident of Mahesh
b. Why LED is a better choice ? Give any two reasons
c. What is doping and explain how it helps in increasing conductivity of an intrinsic semi
conductor?
The number of silicon atom per m3 is 5X1028 . This is doped simultaneously with 5X1022
atoms per m3 . Arsenic and 5X1020 per m3 atoms of Indium. Calculate the number electrons
and holes. Given that ni=1.5X1016 per m3 . Is the material n-type or p-type?
OR
With a neat labeled diagram Explain the working of a Full Wave Rectifier and draw input and
output wave forms. How is it advantageous over a half wave rectifier and what will the output
frequency in Half wave Rectifier and FWR if input frequency fed to HWR &FWR is 60Hz.
27. With a neat labeled diagram explain the working of a NPN or PNP transistor as a common
emitter amplifier. Draw input output wave forms and explain How phase reversal takes place
in output
OR
What is the principle in an Oscillator and explain the working of a transistor as an Oscillator
with the help of a neat labeled diagram?
28. What is a communication system? Describe briefly the major constituents of a
communication system with appropriate block diagrams.