Context: The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.

Question: Why is a transistor so useful?
Answer: gain

Question: What is gain?
Answer: it can act as an amplifier

Question: What is an additional use of the transistor?
Answer: turn current on or off in a circuit

Question: What determines the amount of current in an electrically controlled switch?
Answer: other circuit elements

Question: What controls how strong the output signal is?
Answer: Unanswerable

Question: Where are transistors located?
Answer: Unanswerable

Question: How large is a transistor in comparison to a terminal?
Answer: Unanswerable

Question: What does a signal become when the transistor does not work properly?
Answer: Unanswerable

Question: Where would an electrically controlled switch be located?
Answer: Unanswerable