1.
A semiconductor is irradiated with light such
that carriers are uniformly generated throughout its volume. The semiconductor is
n-type with N

_{D}= 10^{19}cm^{-3}. If the excess electron concentration in the steady state is Δn = 10^{15}cm^{-3}and if τ_{p}= 10 µsec (minority carrier life time), then the generation rate due to irradiation is ………….
2.
A PN junction with a 100 Ω resistor is forward biased so
that a current of 100 mA flows. If the voltage across this combination is
instantaneously reversed to 10 volts at t = 0, the reverse current that flows
through the diode at t = 0 is approximately given by

a.
0 mA

b.
100 mA

c.
200 mA

d.
50 mA

3.
An infrared LED is usually fabricated from

a.
Ge

b.
Si

c.
GaAs

d.
GaAsP

4.
In a transistor having finite β,
the forward bias across the base emitter junction is kept constant and the
reverse bias across the collector base junction is increased. Neglecting the
leakage across the collector base junction and the depletion region generating
current, the base current will………….. (Increase / Decrease / Remains constant).

5.
An n-channel JFET has a pinch off voltage V

_{P}= -5 volts, V_{DSmax}= 20 volts, and g_{m}= 2 mA/V. The minimum ON resistance is achieved in the JFET for …………
6.
The JFET in the circuit shown has an I

_{DSS}= 10 mA and V_{P}= 5 volts. The value of the resistance R_{S}for a drain current I_{DS}of 6.4 mA is …………….. (Select the nearest value).
7.
If the transistors in figure, have high values
of β
and a V

_{BE}of 0.65 volts, the current I flowing through the 2 KΩ resistance will be…………
8.
The 6 volts Zener diode shown in figure has zero
zener resistance and a knee current of 5 mA. The minimum value of R so that the
voltage across it does not fall below 6 volts is ……

**Solution :**https://www.youtube.com/watch?v=j45arOd6cYQ

9.
A PNP transistor shown in figure has uniform
doping in the emitter, base and collector regions, where in the doping
concentrations are 10

^{19}cm^{-3}, 10^{17}cm^{-3}and 10^{15}cm^{-3}respectively. The minority carrier diffusion lengths in the emitter and the base regions are 5 µm and 100µm respectively.
Assuming low level injection conditions and using law of the junction,
calculate the collector current density and the base current density due to
base recombination.

[Suitable approximations may be made if required.]

In all the regions of transistors, D

_{p}= 8 cm^{2}/sec, D_{n}= 16 cm^{2}/sec, n_{i}= 1.5 X 10^{10}cm^{-3}, KT/q = 26 mV and q = 1.6 X 10^{-19}C.**Solution :**

10.
An n-channel MOSFET having a threshold voltage
of 2 volts is used in the circuit shown in figure. Initially the transistor is
OFF and is in steady state. At time t = 0, a step voltage of magnitude of 4
volts is applied to the input so that the MOSFET turns ON instantaneously.

Draw the equivalent circuit and calculate the time taken to the output V

_{o}to fall to 5 volts.
The
device constant of the MOSFET, K = 5 mA/ V

^{2}, C_{DS}=0 and C_{DG}= 0.**Solution :**https://www.youtube.com/watch?v=ccRFcF5_sQQ

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