Answer / badal

SCR Full form of Silicon controlled rectifier.

Answer / vinee

A SCR is a unidirectional device that is applicable in high and medium power applications. It has 4 layers and 3 junctions. A positive gate pulse across gate and cathode turned it on. UJT is used for triggering.

Whereas a TRIAC is a bidirectional device that can be tuned on by applying both positive and negative gate pulses. It is more sensitive than an scr. It is also a 4 layer 3 junction device. DIAC is used for triggering..

They both can be used as lamp dinmers , heat control, speed control of induction motors according to their need.

Answer / engr. asad ali

SCR
It is four layered, three terminal semiconductor device.
The current is unidirectional, flowing only from cathode to anode.
Positive voltage is applied to gate to turn on.
A SCR can be turn off by rvercing current or reduce the voltage of anode below threshold value.
It conduct dc only.

Triac
It consist of two scr connected in opposite directions.
It has two main terminals (i.e 1 and 2) and a gate.
It operate on ac.
it can be turn off as SCR.

i need previous entrence exam papers of nhpc.

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