Physics

Semiconductors and Diodes

461 Questions

Semiconductors and diodes form the foundation of modern electronics, covering topics like intrinsic carrier concentration and Zener breakdown. Questions often explore the characteristics of bipolar junction transistors (BJT) and the properties of doped silicon materials. This topic is crucial for physics and electronics engineering competitive exams.

Zener diode breakdownBJT circuit analysisIntrinsic carrier concentrationDoping in semiconductorsEmitter follower circuit

Semiconductors and Diodes Questions

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

A p-n junction diode cannot be used

  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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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 current through conductors study about cells electric cell types of cells

The longer lead of a LED is always connected to the negative terminal of the battery and the shorter lead is connected to the posltlve terminal of the battery

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.
The LED bulb has two leads. The lead connected to the positive terminal of battery is called anode and the lead connected to the negative terminal is cathode. The slightly longer lead than the other is always connected to the positive terminal and the shorter lead is connected to the negative terminal.
Hence, the given statement is false.

Multiple choice properties of an ideal op-amp electronics physics the operational amplifier (op-amp)

An infinite impedance for an ideal opamp implies

  1. Opamp doesn't draw any current through its terminals

  2. Opamp draws only 10 micro amperes for its function

  3. Opamp's inverting terminal draws no current

  4. Opamp's non inverting terminal draws no current
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Since input impedance for an ideal opamp is infinite, the current drawn will be zero 

Multiple choice properties of an ideal op-amp electronics physics the operational amplifier (op-amp)

A voltage follower 

  1. has a voltage gain of 1

  2. is noninverting

  3. has no feedback resistor

  4. has all of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

a voltage follower is a circuit, wherein the magnitude and the phase of the signal remains the same. In order to achieve it, the feedback signal should be fed to positive terminal, so that phase is unchanged and the absence of a feedback resistor makes no loss in the output signal

Multiple choice ac and dc ac vs dc electro-magnetism effects of electric current physics

A transistor based radio receiver set (effective resistance of the order of 18 ohms) operates on a 9V dc battery. If this replaced by a dc power supply with rating 9V, 500A then:

  1. Receiver will work normally

  2. Receiver will give distorted output

  3. Receiver will get burnt

  4. Power supply will get over heated
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

In this case, the 9 V battery is replaced with a 9 V power supply. Here, there is no change in the power supply to the radio receiver.
Hence, the receiver will work fine as the voltage supply or power supply remains the same.

Multiple choice physics communication system commonly used terms in electronic communication system elements of communication system electromagnetic waves and communication system

Thermal noise is generated in:

  1. transistors and diodes

  2. resistors

  3. copper wire

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Thermal noise or Nyquist noise is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.

In each of the options, an electrical element is used and hence this noise is produced in all these elements. The correct option is option D

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

Zener breakdown takes place if:

  1. Doped impurity is low

  2. Doped impurity is high

  3. Less impurity in N-part

  4. Less impurity in P-type
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

 Zener breakdown occurs due to heavily doped diodes.In this process electrons crosses the barrier from 

the valence band of the p-type  to the conduction band of the lightly filled n-type material.

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

The main cause of Zener breakdown is

  1. the base semiconductor being germanium.

  2. production of electron-hole pairs due to thermal excitation.

  3. low doping.

  4. high doping.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Zener breakdown occurs in heavily doped p-n junctions. The heavy doping makes the depletion layer extremely thin. So that, carriers cannot accelerate enough to cause ionization. Thus, current will increase in reverse bias only due to reverse breakdown voltage.

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

The main cause of avalanche breakdown is

  1. collision by ionisation.

  2. high doping.

  3. recombination of electrons and holes.

  4. low doping.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Avalanche breakdown is caused by impact ionization of electron-hole pairs. A very little current flows under reverse bias conditions and depletion region increases. The electric field in the depletion region of a diode can be very high. Electron/holes that enter the depletion region undergo a tremendous acceleration. As these accelerated carriers collide with the atoms, they can knock electrons from their bonds, creating additional electron/hole pairs and thus additional current. As these secondary carriers are swept into the depletion region, they too are accelerated and the process repeats itself.

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

The avalanche breakdown in p-n junction is due to

  1. shift of Fermi level.

  2. cumulative effect of conduction band electron.

  3. widening of forbidden gap.

  4. high impurity concentration.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The avalanche breakdown in p-n junction is due to cumulative effect of conduction band electron. In reverse bias, due to applied electric field, electrons acquire enough energy to free more electron bound to the atom. The abundant number of electron-hole pairs are created for conduction, this is cumulative effect.