1.

The current gain of a transistor in common emitter configuration is 70. If emitter is 8.8 mA, then find (i) base current (ii) collector current. (iii) the current gain in common base configuration.

Answer»

Solution :`"Current gain, "beta=(I_(C ))/(I_(B)), I_(E)=I_(B)+I_(C )`
(i) `I_(C )=betaI_(B)"or"I_(C )=70I_(B)`
`"Since "I_(E)=I_(B)+I_(C )"or"I_(E)=I_(B)+70I_(B)`
`orI_(E)=71I_(B)`
`therefore I_(B)=(I_(E))/(71)=(8.8)/(71)=0.124mA`
(ii) Collector current `=I_(C)`
`I_(C )=70I_(B) or I_(C )=70xx0.124=8.68mA`
(III) Current gain in common BASE configuration
`ALPHA=(beta)/(1+beta) or alpha=(70)/(71)=0.986`


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