Tag: electric circuits

Quizzes (8) Questions (30)

Questions Related to electric circuits

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

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

  1. directed biased

  2. unbiased

  3. forward biased

  4. reverse biased
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

For germanium diode, the junction voltage is about _____.

  1. $0.7V$
  2. $0.3V$
  3. $0.6V$
  4. $3V$
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

For detecting the light_______________.

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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).
Multiple choice physics electric circuits introduction to diodes circuit components junction diode and its voltage current characteristics

Select the correct statement from the following 

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A diode allows current to flow in only one direction, which is the fundamental principle behind rectification, converting AC to DC.

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

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 

  1. 200 $\Omega$
  2. 400 $\Omega$
  3. 40 $k\Omega$
  4. 4 $k\Omega$
Reveal answer Fill a bubble to check yourself
B Correct answer
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

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

When a diode is heavily doped the 

  1. Zener voltage will be low

  2. Avalanche voltage will be high

  3. Depletion region will be thin

  4. Leakage current will be low
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $r _ { p } \propto I _ { p }$
  2. $r _ { p } \propto I _ { p } ^ { 3 / 2 }$
  3. $r _ { p } \propto \frac { 1 } { I _ { p } }$
  4. $r _ { p } \propto \frac { 1 } { \left( I _ { p } \right) ^ { 1 / 3 } }$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In a vacuum diode operating in the space charge limited region, Langmuir-Child law states that plate current Ip is proportional to V^(3/2). Dynamic plate resistance rp = dV/dIp. Differentiating the relation gives rp proportional to 1/(Ip^(1/3)).

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

Zener diode is used as

  1. Half wave rectifier

  2. Full wave rectifier

  3. ac voltage stabilizer

  4. dc voltage stabilizer
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A Zener diode is specially designed to operate reliably in the breakdown region under reverse bias. Because the voltage across it remains nearly constant over a wide range of reverse currents, it is widely used as a dc voltage regulator or stabilizer.