Electric & Devices Applications

midterm 2

In which region does BJT act as the OFF switch in electronic circuits?

a) Cut-off
b) Saturation
c) Active
d) Reverse saturation

(A) In the saturation region, the emitter-base junction is forward biased, the collector-
base junction is also forward biased. This is the operating mode when no current flows through
BJT

The state of a BJT in which the collector current has reached a maximum and is independent
of the base current

Saturation

In which region does BJT act as the OFF switch in electronic circuits?

a) Cut-off
b) Saturation
c) Active
d) Reverse saturation

(A) In the saturation region, the emitter-base junction is forward biased, the collector-
base junction is also forward biased. This is the operating mode when no current flows through
BJT

The state of a BJT in which the collector current has reached a maximum and is independent
of the base current

Saturation

The process of increasing the power, voltage, or current by electronic means.

floating point
bipolar
AND gate
Amplification

(d) Amplification

Characterized by a linear process in which a variable takes on a continuous set of values.

Analog

One of the semiconductor regions in a BJT. The base is very thin and lightly doped compared
to the other regions

Base

The ratio of dc collector current to dc emitter current in a bipolar junction transistor.

Alpha

In a PN junction with no external voltage, the electric field between acceptor and donor ions is
called a

A. Peak
B. Barrier
C. Threshold
D. Path

(b)

In a PN junction the potential barrier is due to the charges on either side of the junction,
these charges are

A. Majority carriers
B. Minority carriers
C. Both (a) and (b)
D. Fixed donor and acceptor ions

(B) minority carries

The capacitance of a reverse biased PN junction
A. Increases as reverse bias is increased
B. Decreases as reverse bias is increased
C. Increases as reverse bias is decreased

D. insignificantly low

( c )

In an unbiased PN junction
A. The junction current is due to minority carriers only
B. The junction current at equilibrium is zero as equal but opposite carriers are crossing the
junction
C. The junction current reduces with rise in temperature
D. The junction current at equilibrium is zero as charges do not cross the junction

( b ) the junction current at equilibrium is zero as equal but opposite carriers are crossing the junction

What type of device is a diode?
a) Unidirectional
b) Bidirectional
c) Isolated

d) inappropriate

(a)
Explanation: Diode is a device which allows current to flow only in one direction with ease. In
the opposite direction, it far more difficult to conduct current for the diode. So, it can’t be
acknowledged as a bidirectional device as that changes the properties and characteristics of
diode. Hence, Diode is a unidirectional device

Which region of the diode, does the anode corresponds to?
a) N-type
b) P-type
c) Depletion layer
d) Hidden

b
Explanation: When the diode is biased by an external source, the anode is connected to the
positive terminal and cathode to the negative terminal. P-type material has majority carriers as
holes. If a potential difference is applied externally, the electrons in N-type would flow in a
direction N-P i.e. cathode to anode and the direction of current would be from anode to cathode

What is the voltage required across the P-N junction, to make it conduct in forward bias state
for a silicon diode?
a) 0.3 V
b) 0.9 V
c) 0.7 V
d) 1.2 V

( c )
Explanation: The forward biasing voltage is the voltage, which is applied across the P-N junction
externally to make flow of current with ease. In forward biased state the anode is connected to
positive terminal and cathode to the negative terminal of the external supply. Such voltage for
Silicon diode is 0.7 Volts and for Germanium is 0.3 Volts

If the voltage across the Diode is 0.7 Volts and the rating of battery is 7 Volts, 1 Ampere then, what will the bulb do?

a) Defuse
b) Remain off

c) Partially glow
d) Glow

( d )
Explanation: As seen in the figure, it is clear that the diode is forward biased and the voltage
across the diode is 0.7 Volts, which the forward biasing voltage, due to which the current will
flow and the bulb will glow. But, if the diode was reverse biased then even if we apply 0.7 volts
the bulb would not have glowed.

When voltage is applied across cathode to anode then it is said to be ________ biased

a) Reverse
b) Forward
c) Cyclic
d) Backward

Answer: b
Explanation: When we apply a voltage across a reversed diode i.e. we are applying from cathode
to anode (N-type to P-type). The diode is said to be reverse biased in this state, in which, it can
resist current up to a certain limit depending on the physical conditions

Name the maximum voltage that the diode can withstand, when a reverse bias voltage is
applied to it.

a) Peak Voltage
b) Minimal Voltage
c) Peak Inverse Voltage
d) Minimal Inverse Voltage

( c )
Explanation: When a reverse bias voltage is applied to a diode that means, we will connect the
anode to negative point and cathode to positive point of an external potential difference. It can
only withstand a voltage up to a certain limit. If the limit is crossed it undergoes breakdown
called as Reverse voltage breakdown and that value is the Peak Inverse Voltage

Which state of the graph shows the I-V characteristics of the diode?

a) Forward biased

b) Peak Voltage
c) Conducting state
d) Reverse Biased

Answer: d
Explanation: As seen the graph we can observe that the values of current and voltage are
negative. It clearly describes about the reverse bias state of diode, as it also shows the reverse
breakdown and the Peak Inverse Voltage. The immediate declination of voltage after a point, is
the breakdown.

How is the depletion layer in forward biased state as compared to reverse biased state?
a) Thin
b) Thick
c) Absent
d) Maximum

a
Explanation: When the diode is forward biased, the electron from the N-type move to P-type
much quicker than when they are in natural state. The external potential difference applied
allows the diode to get to equilibrium sooner and also reduces the potential barrier. This creates
an easy path for the flow of current, which make the depletion layer thin.

How is the resistance in the reversed biased state, as compared to the forward biased state
resistance?

a) Low
b) High
c) Moderate
d) Same

b
Explanation: When the diode is in reversed bias state, the depletion layer is thick than the
depletion layer formed in the forward biased state. Due to the external potential applied it adds
up to the barrier made naturally in the depletion layer. This reduces the flow of current to great
extent and hence the diode acts as an insulator and end up with high resistance

What is the magnitude of the current in forward biased state?
a) Zero
b) Depends on reverse voltage
c) Depends on forward voltage
d) Depends on temperature

c
Explanation: The magnitude of the current can’t be zero, as there will be a least current passing
through the diode. Also, the value depends on the reverse saturation current and not the reverse
voltage. The effect of temperature does affect the current but is not dependent on it. So, the
magnitude depends on the forward biasing voltage.

A reverse-biased silicon diode has about 0.7 V across it. T/F

False

An atom is the smallest particle of an element that retains the characteristics of that element.
T/F

True

An intrinsic semiconductor is neither a good conductor nor a good insulator. T/F

True

A pn structure is called a diode. T/F

True

An intrinsic crystal is one that contains a small amount of impurities. T/F

False

N-type semiconductor material has very few free electrons. T/F

False

The silicon material used in semiconductors is extremely pure with no additives. T/F

True

The movement of free electrons in a semiconductor material is termed electron voltage. T/F

False