After a transistor has been biased with the Q point near the middle of
the load line, we can couple a small ac voltage into the base. This will
produce an ac collector voltage. The ac collector voltage looks like the
ac base voltage, except that it’s a lot bigger. In other words, the ac
collector voltage is an amplified version of the ac base voltage.
The invention of amplifying devices, first vacuum tubes and later
transistors, was crucial to the evolution of electronics. Without
amplification, there would be no radio, no television, and no
computers.
