Electronic Devices - Online Test
Q1. In a forward biased pn junction diode, the sequence of events that best describes the mechanism of current flow is
Answer : Option A
Explaination / Solution:
The potential barrier of the pn junction is lowered when a forward bias voltage is applied, allowing electrons and holes to flow across the space charge region (Injection) when holes flow from the p region across the space charge region into the n region, they become excess minority carrier holes and are subject to diffuse, drift and recombination processes.
Hence correct option is (A)
Q2. In IC technology, dry oxidation (using dry oxygen) as compared to wet oxidation (using steam or water vapor) produces
Answer : Option D
Explaination / Solution:
In IC technology, dry oxidation as compared to wet oxidation produces superior quality oxide with a lower growth rate
Q3.
In a MOSFET operating in the saturation region, the channel length modulation effect causes
Answer : Option D
Explaination / Solution:
In a MOSFET operating in the saturation region, the channel length modulation effect causes a decrease in output resistance.
Q4. In the circuit shown below, capacitors C1 and C2 are very large and are shorts
at the input frequency. vi is a small signal input. The gain magnitude 
at 10
M rad/s is
at 10
M rad/s is
Answer : Option A
Explaination / Solution:
For the parallel RLC circuit resonance frequency is,
which is maximum
Thus given frequency is resonance frequency and parallel RLC circuit has
maximum impedance at resonance frequency
Gain of the amplifier is 
where ZC is impedance of parallel RLC
circuit.
where ZC is impedance of parallel RLC
circuit.Hence at this frequency (ωr), gain is
which is maximumTherefore gain is maximum at ωr = 10 /sec M rad .
Q5. Drift current in the semiconductors depends upon
Answer : Option C
Explaination / Solution:
No Explaination.
Q6. A Zener diode, when used in voltage stabilization circuits, is biased in
Answer : Option B
Explaination / Solution:
Zener diode operates in reverse breakdown region.
Q7. A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10ºC, the forward bias voltage across the PN junction
Answer : Option D
Explaination / Solution:
For every 1º C increase in temperature, forward bias voltage across diode decreases by 2.5 mV. Thus for 10º C increase, there us 25 mV decreases
Q8. In the circuit shown below, for the MOS transistors, 
and
the threshold voltage VT = 1 V. The voltage Vx at the source of the upper
transistor is
and
the threshold voltage VT = 1 V. The voltage Vx at the source of the upper
transistor is
Answer : Option C
Explaination / Solution:
Given circuit is shown below.
Thus our assumption is true and Vx = 3 V.
For transistor M2,
Since 
thus M2 is in saturation.
By assuming M1 to be in saturation we have
thus M2 is in saturation.
By assuming M1 to be in saturation we haveTaking positive root,
Thus our assumption is true and Vx = 3 V.
Q9. For a BJT the common base current gain α = 0.98 and the collector base
junction reverse bias saturation current ICO = 0.6 μA. This BJT is connected in
the common emitter mode and operated in the active region with a base drive
current IB = 204 A. The collector current IC for this mode of operation is
Answer : Option D
Explaination / Solution:
In active region, for common emitter amplifier,
Substituting ICO = 0.6 μA and IB = 204 μA in above eq we have,
IC = 1.01 mA
Q10. For the BJT QL in the circuit shown below, 
The
switch is initially closed. At time t = 0, the switch is opened. The time t at
which Q1 leaves the active region is
The
switch is initially closed. At time t = 0, the switch is opened. The time t at
which Q1 leaves the active region is
Answer : Option C
Explaination / Solution:
Applying KCL at collector
with time, the capacitor charges and voltage across collector changes from 0
towards negative.
