What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?

Answer: D. Alpha cutoff frequency

Alpha is the grounded-base (common-base) current gain. The frequency where alpha drops to 0.707 of its low-frequency value is the alpha cutoff frequency. Beta cutoff refers to the grounded-emitter gain.

Tip: Grounded base = alpha; drop to 0.7 = cutoff.