The a-c current gain of a transistor is `beta=19`. In its common-emitter configuration, what will be the change in the collector-current for a change of 0.4 mA in the base-current? What will be the change in the emitter current?

Explanation

By definition, the a-c current gain `beta` is given by
`beta_(ac)=(DeltaI_(C))/(DeltaI_(B))`
`:. DeltaI_(C)=betaxxDeltaI_(B)=19xx0.4mA=7.6mA`.
The emitter-current is the sum of the base-current and the collector-current `(i_(E)=i_(B)+i_(C))`
`:. DeltaI_(E)=DeltaI_(B)+DeltaI_(C)=0.4mA+7.6mA=80mA`.