Power Electronics
An SCR is considered to be a semi controlled device because

 it can be turned ON only during one half cycle of an AC.
 it can be turned OFF but not ON with a gate pulse.
 it conducts only during one half cycle of an alternating current wave.
 it can be turned ON but not OFF with a gate pulse.

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Power Electronics
Rise time is defined by the interval when

 anode current rises 10 % to 90 % of its final value.
 gate current rises from 90 % to 100 % of it final value.
 anode voltage drops from 90 % to 10 % of its initial value.
  both B and C.

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