Figure shows four electronic switches $$(i), (ii), (iii)$$ and $$(iv).$$ Which of the switches can block voltages of either polarity (applied between terminals $$‘a’$$ and $$‘b’$$) when the active device is in the OFF state?

The typical ratio of latching current to holding current in a $$20$$ $$A$$ thyristor is

Circuit turn-off time of an $$SCR$$ is defined as the time

Figure shows a composite switch consisting of a power transistor $$(BJT)$$ in series with a diode. Assuming that the transistor switch and the diode are ideal, the $$I$$-$$V$$ characteristic of the composite switch is