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CBSE CLASS 12 PHYSICS – Semiconductor Physics: Test
Name:
School:
Max. Score: 35
Duration: 60 min
Batch:
1. In a transistor, the doping level is slightly increased. How will affect the (a) collector
current and (b) base current? (2)
2. How will the collector current change if the base is widened? (1)
3. Sn, C, Si and Ge are in the same group (14th). Yet only Si and Ge are considered
semiconductors. Explain. (2)
4. Zener diodes have high dopant densities. What effect does it have on the (a) depletion layer
and (b) junction field? Draw the circuit for a Zener diode as an voltage regulator. (2)
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5. Identify the logic gates in the logic circuit shown below. Complete the truth table below for
the circuit. (3)
6. In the circuit shown below, the resistor R1 is increased. How will the readings on the
ammeter and voltmeter change? (2)
7. For a CE-transistor amplifier, the audio signal voltage across the collected resistance of
2 kΩ is 2 V. Suppose the current amplification factor of the transistor is 100, find the input
signal voltage and base current, if the base resistance is 1 kΩ. (2)
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8. Construct AND, OR and NOT gates using NAND gates only. (3)
9. The figure shows the I – V characteristics of a PN diode. Determine the dc and ac
resistances of the diode when it operates at 0.3 V. (2)
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10. A semiconductor has equal electron and hole concentration of 2 x 108 m-3. On doping with
a certain impurity, the hole concentration increases to 4 x 1010 m-3. (2)
(a) What type of semiconductor is obtained by this type of doping?
(b) Calculate the electron concentration after doping.
(c) How does the energy gap change as a result of this doping?
11. A semiconductor has electron and hole concentrations as 0.45 x 1012 m-3 and 5 x 1020 m-3
respectively. Determine its conductivity if: hole mobility = 0.048 m2V-1s-1; electron
mobility = 0.135 m2V-1s-1; electron charge = 1.6 x 10-19 C. (2)
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12. What is an amplifier? Explain the action of a NPN transistor amplifier in the CE mode. Does
an amplifier violate energy conservation? Draw the frequency response curve of
(a) practical transistor amplifier and (b) ideal amplifier. Two amplifiers are connected one
after the other in series (cascaded). The first amplifier has a voltage gain of 10 and the
second has a voltage gain of 20. If the input signal is 0.01 volt, calculate the output ac
signal. (6)
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13. A square wave (-1 V to +1 V) is applied across a PN junction diode. Draw the output
waveform across the diode assuming the diode to be ideal. (1)
14. In the circuit below, a source of 2 V is connected. Determine the currents that may be
drawn from the source.
15. Suggest suitable materials for solar cells. (1)
16. Identify the type of transistor shown in the figure below. Is the transistor properly biased?
(2)