Test: Electronic Devices And Circuits - 4

QUESTION: 1

An increase in junction temperature of a semiconductor diode

A.
causes a small increase in reverse saturation current
B.
causes a large increase in reverse saturation current
C.
does not affect reverse saturation current
D.
may cause an increase or decrease in reverse saturation current depending on rating of diode

Solution:

Reverse saturation current doubles for every 10ºC rise in junction temperature.

QUESTION: 2

An air gap provided in the iron core of an inductor prevents

A. flux leakage
B. hysteresis loss
C. core saturation
D. heat generation

Solution:

QUESTION: 3

Generally, the gain of a transistor amplifier falls at high frequency due to the

A. internal capacitance of the device
B. coupling capacitor at the I/P
C. skin effect
D. coupling capacitor at the O/P

Solution:

QUESTION: 4

Which of these has a layer of intrinsic semiconductor?

A. Zener diode
B. PIN diode
C. Photo diode
D. Schottky diode

Solution:

The intrinsic layer is in between p and n layers.

QUESTION: 5

Assertion (A): When Diode used as rectifier the reverse breakdown voltage should not be exceeded.

Reason (R): A high inverse voltage can destroy a p-n junction.

A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Solution:

PIV is an important parameter in rectifier operation.

QUESTION: 6

A Si sample is doped with a fixed number of group N impurities. The electron density n is measured from 4 K to 1200 k for the sample. Which one of the following is correct?

A. n remains constant over the temperature range
B. n increases monotonicaliy with increasing temp
C. n increases first remains constant over a range and again increases with increasing temperature
D. n increases show a peak and then decrease with temperature

Solution:

QUESTION: 7

Assertion (A): In design of circuit using BJT, a derating factor is used.

Reason (R): As the ambient temperature increases, heat dissipation becomes slower.

A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Solution:

Increase of ambient temperature lowers the heat dissipation capacity.

Therefore derated operation of BJT is necessary lest BJT should be destroyed.

QUESTION: 8

If the drift velocity of holes under a field gradient of 100 V/m is 5m/sec. Their mobility is

A. 0.05
B. 0.5
C. 50
D. 500

Solution:

E = μ . V_d μ =.

QUESTION: 9

In a P type silicon sample, the hole concentration is 2.25 x 10¹⁵ / cm³. If the intrinsic carrier concentration is 1.5 x 10¹⁰/ cm³ the electron concentration is

A. zero
B. 10¹⁰/cm³
C. 10⁵/cm³
D. 1.5 x 10²⁵/cm³

Solution:

Electron concentration .

QUESTION: 10

The behaviour of a JFET is similar to that of

A. NPN transistor
B. PNP transistor
C. SCR
D. Vacuum triode

Solution:

Both JFET and vacuum triode are voltage controlled devices.

QUESTION: 11

What is the effect of cut in voltage on the wave form of output as compared to input in a semiconductor diode?

A.
The duration of output waveform is less than 180º
B.
Output voltage is less than input voltage
C.
Output voltage is more than input voltage
D.
Both (a) and (b)

Solution:

Since the duration of output waveform is less than 180º, output voltage is less than input voltage.

QUESTION: 12

As temperature increases the number of free electrons and holes in an intrinsic semiconductor

A. increases
B. decreases
C. remains the same
D. may increase or decrease

Solution:

Increase of temperature increases conductivity of semiconductors.

QUESTION: 14

Assertion (A): A JFET behaves as a resistor when V_GS < V_P.

Reason (R): When V_GS < V_P, the drain current in a JFET is almost constant.

A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Solution:

QUESTION: 15

In a reverse biased P-N junction, the current through the junction increases abruptly at

A. zero voltage
B. 1.2 V
C. 0.72 V
D. breakdown voltage

Solution:

QUESTION: 17

Resistivity of hard drawn copper is

A. less than that of annealed copper
B. more than that of annealed copper
C. same as that of annealed copper
D. decreasing when temperature increases

Solution:

QUESTION: 18

The channel of JFET consists of

A. p type material only
B. n type material only
C. conducting material
D. either p or n type material

Solution:

The channel in JFET may be n type or p type. If channel is n type, gate is p type and if channel is p type gate is n type.

QUESTION: 19

In a bipolar junction transistor a_dc = 0.98, I_CO= 2 μA and 1_B = 15 μA. The collector current I_C is

A. 635 mA
B. 735 mA
C. 835 mA
D. 935 mA

Solution:

QUESTION: 20

The voltage across the secondary of the transformer in a half wave rectifier with a shunt capacitor filter is 50 volts. The maximum voltage that will occur on the reverse biased diode will be

A. 100 V
B. 88 V
C. 50 V
D. 25 V

Solution:

QUESTION: 21

Assertion (A): The forward resistance of a p-n diode is not constant.

Reason (R): The v-i characteristics of p-n diode is non-linear.

A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true

Solution:

If v-i characteristics is non linear, the ratio v-i is not constant.

QUESTION: 22

For a photoengraving the mask used is

A. master mask
B. slave mask
C. working mask
D. photo mask

Solution:

The mask that is prepared first is called the master mask made from glass substrates covered by thin chromium film.

From the master masks are prepared working masks by contact pointing and used for Photolithography which means Photo engraving.

QUESTION: 23

In a varactor diode the increase in width of depletion layer results in

A. decrease in capacitance
B. increase in capacitance
C. no change in capacitance
D. either (a) or (b)

Solution:

Capacitance is inversely proportional to distance between plates.

QUESTION: 24

In given figure a silicon diode is carrying a constant current of 1 mA. When the temperature of the diode is 20ºC, V_D is found to be 700 mV. If the temperature rises to 40ºC, V_D becomes approximately equal to