Tag: electronic devices

Questions Related to electronic devices

Select and write the correct option from the options given in each question:
Optical Detector is:

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Diode Laser

  2. Laser

  3. LED

  4. Photo Diode

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Correct Option: D

Which of the following is/are true regarding  breakdown voltage of Zener diode?

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. If the reverse bias voltage across a p-n junction diode is increased, at a particular voltage the reverse current suddenly decreases to a large value

  2. The holes in the n-side and the conduction electrons in the p-side are accelerated due to the reverse bias voltage.

  3. The voltage at which the rate of creation of hole-electron pairs is increased leading to the increased current is called avalanche breakdown

  4. None of the above

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Correct Option: B
Explanation:

Consider applying an external voltage to the junction with the the negative terminal connected to the P type material and the positive terminal connected to the N type material. For the P-N junction this would require injecting electrons into the P type material. These electrons would recombine with holes and therefore further deplete the majority charge carriers in the P type semiconductor. 


Also removing electrons from the N type material would obviously cause further depletion the free electrons (the majority charge carriers in the N type semiconductor). This causes a widening of the depletion layer and an increase in the charge at the junction which reinforces the barrier voltage to oppose the applied voltage. The net result is that when the P-N junction is reversed biased it blocks current flow.

Which of the following semi-conducting devices is used as voltage regulator?

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Zener diode

  2. LASER diode

  3. Photo diode

  4. Solar cell

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Correct Option: A
Explanation:

Zener diode is used as a voltage regulator device because the voltage across the zener diode in reverse bias is constant after reaching certain value i.e. breakdown voltage.

What is true about the breakdown voltage in a zener diode?

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. It decreases when current increases.

  2. It destroys the diode.

  3. It equals the current times the resistance.

  4. It is approximately constant.

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Correct Option: D
Explanation:

As the current in the zener diode increases, the voltage across the diode remains constant. This voltage will be equal to the zener breakdown voltage

When the source voltage increases in a zener regulator, which of these currents remains approximately constant?

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Series current

  2. Zener current

  3. Load current

  4. Total current

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Correct Option: C
Explanation:

The load current is independent of the source voltage variations and hence remains a constant

If the load resistance decreases in a zener regulator, the zener current

zener diode special purpose diodes electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. Decreases

  2. Stays the same

  3. Increases

  4. Equals the source voltage divided by the series resistance

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Correct Option: C
Explanation:

The load current is given by $I _L=\dfrac{V _z}{R _L}$ and the zener current is given by $I _z=I _s-I _L$. Thus, if the load resistance decreases, load current increases. This in turn will reduce the zener current 

The input resistance of a silicon transistor is $1 k\Omega $.If base current is changed by $100 \mu A$ it causes the change in collector current by $2 mA$. This transistor is used as a CE amplifier with a load resistance of $5 k\Omega$ What is the ac voltage gain of amplifier?

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $10$

  2. 44100$

  3. $500$

  4. $200$

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Correct Option: D

In a silicon transistor the base current is changed by $25\mu A$. This results in a change of $0.04\ V$ in the base to emitter voltage and a change of $4\ mA$ in the collector current. The trans-conductance of the transistor (in $\Omega^{-1}$) is

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $0.1$

  2. $1$

  3. $1000$

  4. $0.01$

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Correct Option: C

For a common emitter configuration, If $\alpha $and $\beta $ have thier usual meanings. The incorrect relationship between $\alpha $and $\beta $ is:

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $\alpha =\dfrac { \beta }{ 1-\beta } $

  2. $\alpha =\dfrac { \beta }{ 1+\beta } $

  3. $\alpha =\dfrac { { \beta }^{ 2 } }{ 1+{ \beta }^{ 2 } } $

  4. $\dfrac { 1 }{ \alpha } =\dfrac { 1 }{ \beta } +1$

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Correct Option: B,D

For a common emitter connection the values of constant collector current and base current are $5\ mA$ and $50$$\mu A$ respectively. The current gain will be

transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

  1. $10$

  2. $20$

  3. $40$

  4. $100$

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Correct Option: D
Explanation:

Given that:
$I _c = 5\ mA$
$I _b = 50\ \mu A = 5 \times 10^{-2}\ mA$
The current gain is
$\beta = \dfrac{I _c}{I _b}$
$\beta = \dfrac{5}{5 \times 10^{-2}} = 100$