SOLUTION

The triac can be triggered in each mode, but some modes require more or less gate current, than others. Gate is less sensitive and sensitivity varies in different modes. Its switching turn-off time is more and dv/dt rating is less than SCR. Thus it is not suitable for inductive and high-frequency load circuits. Normally, it is used in an ac circuit for high power factor loads and operated at mains frequency (50 or 60 Hz) or frequency below 400 Hz. Since the triac can conduct in either direction, forced commutation by reverse-biasing cannot be employed. So turn-off is either by current starvation, which is usually impractical, or else by ac line commutation.