This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Zenner Diode”.
1. Zener diode is designed to specifically work in which region without getting damaged?
a) Active region
b) Breakdown region
c) Forward bias
d) Reverse bias
Explanation: The Zener diode is a specifically designed diode to operate in the breakdown region without getting damaged. Because of this characteristic, it can be used as a constant-voltage device.
2. What is the level of doping in Zener Diode?
a) Lightly Doped
b) Heavily Doped
c) Moderately Doped
d) No doping
Explanation: A Zener diode is heavily doped so that the breakdown voltage occurs at a lower voltage. If it were lightly/moderately doped, it would breakdown at a comparatively high voltage and, thus, would not be able to serve its purpose.
3. When the reverse voltage across the Zener diode is increased _____________
a) The value of saturation current increases
b) No effect
c) The value of cut-off potential increases
d) The value of cut-off potential decreases
Explanation: As the frequency of the incident radiation increases, the kinetic energies of the emitted electron are higher and therefore require more repulsive force to be applied to stop them.
The value of saturation current increases, as the intensity of the incident radiation, increases.
The value of cut-off potential decreases, as the frequency decreases.
4. Zener Diode is mostly used as ____________
a) Half-wave rectifier
b) Full-wave rectifier
c) Voltage Regulator
Explanation: The Zener diode, once in the breakdown region, keeps the voltage in the circuit to which it is connected as constant. Thus it is widely used as a voltage regulator.
Explanation: The following figure is the correct symbol for the Zener diode.
The following figure is the symbol of a normal p-n junction diode.
6. In normal junctions, the breakdown is same as Zener breakdown.
Explanation: In normal p-n unction diodes, the breakdown takes place by avalanche breakdown which is different than the Zener breakdown. Zener diode is specifically made to operate in that region.
7. The depletion region of the Zener diode is ____________
c) Very Thin
d) Very thick
Explanation: Zener diode is fabricated by heavily doping both p- and n-sides of the junction, which results in an extremely thin depletion region.
8. The electric field required for the field ionization is of what order?
a) 104 V/m
b) 105 V/m
c) 106 V/m
d) 107 V/m
Explanation: In a Zener diode, a very high electric field is produced for even a very small voltage. The electric field required for field ionization is of the order 106 V/m.
9. In a circuit the load current is 5 mA and the unregulated output is 10 V. If the voltage drop across the Zener diode is 3 V, what should be the value of resistance?
a) 50 Ω
b) 100 Ω
c) 125 Ω
d) 150 Ω
Explanation: The value of R should be such that the current through the Zener diode is much larger than the load current.
Imagine, Iz = 20 mA. The total current is therefore 24 mA.
The voltage drop = 3 V
Resistance = 3 V/24 X 10-3 A
Resistance = 125 Ω.
Explanation: In the absence of Zener diode, the open circuit voltage, V = RlVi/ R + Rl
V = 80 V
Now, since the breakdown voltage of the Zener diode is 50 V, the diode will undergo breakdown
Output Voltage would be equal to 50 V.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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