Electronics and Communication Engineering - Electronic Devices and Circuits

26.
A Varactor diode has
a fixed capacitance
a fixed inductance
a voltage variable capacitance
a current variable inductance
Answer: Option
Explanation:

The applied bias governs the width of depletion layer. Therefore, capacitance varies with bias.


27.
The most important set of specifications of transformer oil includes
dielectric strength and viscosity
dielectric strength and flash point
flash point and viscosity
dielectric strength, flash point and viscosity
Answer: Option
Explanation:

Oil used in transformer work as cooling as well as dielectric strength.


28.

Assertion (A): In Hall effect the O.C. transverse voltage developed by a current carrying semiconductor with a steady magnetic field perpendicular to the current direction has opposite signs for n and p semiconductors.

Reason (R): The magnetic field pushes both holes and electrons in the same direction.

Both A and R are true and R is correct explanation of A
Both A and R are true but R is not a correct explanation of A
A is true but R is false
A is false but R is true
Answer: Option
Explanation:

Holes and electrons move in opposite directions. Therefore R is wrong.


29.
A voltage of 9 V is applied in forward direction to a semiconductor diode in series with a load resistance of 1000 Ω. The voltage across the load resistance is zero. It indicates that
diode is short circuited
diode is open circuited
resistor is open circuited
diode is either o.c or s.c
Answer: Option
Explanation:

Since there is no voltage across load resistor, the current is zero and diode is open-circuit. If diode is short- circuited or resistor is open-circuited almost 9 V will appear across resistor.


30.
If the drift velocity of holes under a field gradient of 100 V/m in 5 m/s, their mobility (in SI units) is
0.05
0.5
50
500
Answer: Option
Explanation:

.