Que-Ans: 10-30 words

[1]        Explain what is a pn junction?

The contact surface between the layers of ptype and n type semiconductor pieces plated together so as to form a pn junction is called the pn junction.

[2]        What are the properties of operational amplifiers (normally used in analog circuits)?

High input impedance, high gain and low output impedance.

[3]        What is the function of not gate in a logic circuit?

It reverses the input logic condition.

[4]        What is a rectifier?

A rectifier is one which converts alternating quantity into unidirectional quantity. (ac to dc).

[5]         Give two advantages of bridge rectifier?

1. Peak inverse voltage rating per diode is less.
2. Centre tapped transformer is not required.

[6]         What are the applications of Zener diode?

Zener diode can be used as a voltage regulator, peak clipper and also used for meter protection, on tankers for intrinsically safe circuits.

[7]        What is meant by firing and commutation of Thyristor?

Firing means bringing SCR from off state to on state. Commutation means making the SCR to go to off state from on state.

[8]        What is a photoelectric device?

It is a device which converts light energy into electrical energy.

  30-60 words

[1]         What features can high specification electronic relays provide?

The features that high specification electronic relays can provide are;

Thermal overload protection with adjustable time / current characteristics.

Overload alarm.

High set over current protection.

Zero phase sequence or earth fault protection.

Negative phase sequence or phase unbalanced protection.

Under current protection.

[2]        What is a semiconductor?’

A semiconductor is one whose property lies between conductor and insulator, in terms of energy bands, semiconductor is one which has almost an empty conduction band and an almost filled valence band with a very narrow energy gap.

[3]         What is meant by doping?

The process of adding impurity to the semiconductor is called doping. If a pentavalent impurity is added we get n type semiconductor. If a trivalent impurity is added we get p type semiconductor.

[4]        What is a FET?

FET is a field effect transistor and is a three terminal, unipolar, solid state device. The three terminals are source, drain and gate. In FET, current conduction is either by electrons or holes and controlled by means of an electric field between the gate electrode and conducting channel of the device.

  60-100 words

[1]        In a SCR define the following: (a) break over voltage (b) peak reverse voltage

(c) Holding current (d) forward current rating (e) Latching current

Break over voltage is the minimum forward voltage at which SCR starts conducting (with Gate terminal open)

Peak reverse voltage: the maximum reverse voltage that can be applied to SCR in the Reverse direction (with conducting)

Holding current: the minimum value of anode current below SCR to off state from on state.

Forward current rating: the maximum anode current withstanding without getting damaged,

Latching current: it is the minimum value of anode current that an SCR must attain during Turn-on, to maintain conduction, when the gate signal is removed.