# Transistor gain problem

felipenavarro

## Homework Statement

If a transistor circuit is used to amplify a 2.5 mA signal to at least
0.1 A, what must be the minimum gain of the transistor circuit?

b. Assume the amplifier consists of a number of transistors in series,
each with a gain of 10. How many transistors are needed in this circuit? (Hint: Two such transistors in series would provide a total gain
of 10 × 10 = 100.)

## Homework Equations

gain current = output current/imput current

## The Attempt at a Solution

for the first question i got that the current gain should be 40,000 by dividing .1 by 2.5*10^-6. i am not sure if this is correct, but if it is then how is it possible to get to 40,000 by multypling tens?(for question b)

Gold Member
2021 Award

## Homework Statement

If a transistor circuit is used to amplify a 2.5 mA signal to at least
0.1 A, what must be the minimum gain of the transistor circuit?

b. Assume the amplifier consists of a number of transistors in series,
each with a gain of 10. How many transistors are needed in this circuit? (Hint: Two such transistors in series would provide a total gain
of 10 × 10 = 100.)

## Homework Equations

gain current = output current/imput current

## The Attempt at a Solution

for the first question i got that the current gain should be 40,000 by dividing .1 by 2.5*10^-6. i am not sure if this is correct, but if it is then how is it possible to get to 40,000 by multypling tens?(for question b)

How many ma are in an amp? How many in .1 amp?

felipenavarro
well 1 million in an amp and 100,000 in .1 amps, so is this the answer for question b? that would be 5 transistors of ten in a row.
but dont i have to get the same answer (as a total amplification) as in question a?

Gold Member
2021 Award
well 1 million in an amp and 100,000 in .1 amps, so is this the answer for question b? that would be 5 transistors of ten in a row.
but dont i have to get the same answer (as a total amplification) as in question a?

Ah, well now see ... THAT'S where your problem is the Greek letter mu is the symbol for micro. The "ma" means MILLIamp, not microamp.

felipenavarro
oh! i dont know why it changed to ma the original problem uses mu i still need help with the problem! haha

Homework Helper
Gold Member
but if it is then how is it possible to get to 40,000 by multypling tens

The question says

If a transistor circuit is used to amplify a 2.5 uA signal to at least 0.1 A

So a gain of 100,000 would also be acceptable.

felipenavarro
ah! got to read with more attention! thanks !