Tag: physics

Questions Related to physics

A p-n junction diode cannot be used

physics electronic devices introduction to diodes circuit components junction diode and its voltage current characteristics

  1. as a rectifier.

  2. for converting light energy to electric energy.

  3. for getting light radiation.

  4. for increasing the amplitude of an AC signal.

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Correct Option: D
Explanation:

To increase the amplitude of an AC signal, transistors are used. p-n junction diodes can be used as rectifiers and in photo-diode and LED.

If ‘p’ region of a semi conductor is connected to negative and ‘n’ region to positive pole, it is said to be

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. directed biased

  2. unbiased

  3. forward biased

  4. reverse biased

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Correct Option: D
Explanation:

In reverse bias, 'p' region of a semi conductor is connected to negative pole and 'n' region to positive pole.

For germanium diode, the junction voltage is about _____.

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. $0.7V$

  2. $0.3V$

  3. $0.6V$

  4. $3V$

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Correct Option: B
Explanation:

The junction voltage $V _{o}$ for a germanium diode is 0.3 V at room temperature. This potential opposes the diffusion of electrons from n-side and holes from p-side. It is 0.7 eV for Si at room temperature.

Diode can work as

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. Modulator

  2. Demodulator

  3. Rectifier

  4. Amplifier

Show answer
Correct Option: C
Explanation:

Diode can work as rectifier, While converting $AC$ voltage to $DC$ voltage, we use $4$ diodes in the form of wheat stone bridge,It effectively works as rectifier.

Therefore option $C$ is correct

For detecting the light_______________.

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. The photodiode has to be forward biased

  2. The photodiode has to be reversed biased

  3. The LED has to connected in forward bias mode

  4. The LED has to be connected in reverse bias mode

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Correct Option: B
Explanation:
Photo diode is used to detect light. 
In reverse biased condition, the width of depletion region increases as the the applied reverse bias voltage increases across the diode. So, by applying a larger voltage, more of the incident photons are converted to electric current thereby increasing the efficiency.
In forward biased condition, the width of depletion region decreases so only a small portion of the incident photons get converted to electric current and hence the efficiency is less.
Hence photo diode in reverse biased condition detects light.
Therefore the correct option is (B).

In a diode detector, output circuit consist of $R=1M\Omega \quad and\quad C=1pF$. Calculate the carrier frequency it can detect.

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. 3000Hz

  2. 1000Hz

  3. 2000Hz

  4. 4000Hz

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Correct Option: B

Select the correct statement from the following 

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. a diode can be used as a rectifier

  2. a diode cannot be used as a rectifier

  3. the current in a diode is always proportional to the applied voltage

  4. None of these

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Correct Option: A

A light emitting diode (LED) has a voltage drop of 2 V across it and passes a current of 10 mA. When it operates with a 6 V battery through a limiting resistor R, the value of R is 

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. 200 $\Omega$

  2. 400 $\Omega$

  3. 40 $k\Omega$

  4. 4 $k\Omega$

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Correct Option: B
Explanation:

Light emitting diode is a forward biased P-N junction which emits light.

The voltage across it = 2 v

Battery voltage = 6 v

Hence total voltage in the circuit = V = 6 - 2 = 4 v

since a LED has 0 resistance in the forward biased region, total resistance in the circuit

= 0 + r = r

current I = 10 mA = 10/1000 A = 0.01 A

we know that,

R = V/I

=> r = 4/0.01 = 400Ω

Hence the value of the limiting resistor is 400Ω

When a diode is heavily doped the 

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. Zener voltage will be low

  2. Avalanche voltage will be high

  3. Depletion region will be thin

  4. Leakage current will be low

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Correct Option: A
Explanation:

The value of reverse voltage at which this occurs is controlled by the amount ot doping of the diode. A heavily doped diode has a low Zener breakdown voltage, while a lightly doped diode has a high Zener breakdown voltage. At voltages above approximately 8V, the predominant mechanism is the avalanche breakdown.

The relation between dynamic plate resistance $\left( r _ { p } \right)$ of a vacuum diode and plate current in the space charge limited region, is 

physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

  1. $r _ { p } \propto I _ { p }$

  2. $r _ { p } \propto I _ { p } ^ { 3 / 2 }$

  3. $r _ { p } \propto \frac { 1 } { I _ { p } }$

  4. $r _ { p } \propto \frac { 1 } { \left( I _ { p } \right) ^ { 1 / 3 } }$

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Correct Option: A