A TRIAC is:

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KVS TGT WET (Work Experience Teacher) Official Paper

Answer 1

TRIAC:

A TRIAC is a bilateral thyristor with three terminals i.e. it can conduct in both directions.
Its three terminals are usually designated as MT1 (Anode 1), MT2 (Anode 2), and the gate by G as in a thyristor.
When in operation, a TRIAC is equivalent to two SCRs conned in antiparallel.
As TRIAC can conduct in both directions, the terms anode, and cathode are not applicable to TRIAC
It is used extensively for the control of power in ac circuits.

The symbol and the i-v characteristics of TRIAC are shown below.

A TRIAC may sometimes operate in the rectifier mode rather than in the bidirectional mode. This may happen due to the following reasons.

For a given value of positive gate current, a TRIAC may turn on with MT2 positive in the first quadrant but may fail to turn on with MT2 negative.
With a constant negative gate current, the TRIAC may turn on with MT2 negative in the third quadrant but may not turn on with MT2 positive.