In the circuit shown, when either A or B is low, what happens to Q1 and Q2?

When either input A or B is low in the described circuit, transistor Q2 becomes active and conducts current, which means it is in an "on" state. This typically occurs in circuits using transistor logic where one transistor can control the state of another. In this scenario, if Q2 is on, it allows current to flow through it, while Q1 remains off since it is not being activated by a sufficient signal or voltage due to either A or B being low.

The operation of Q1 and Q2 depends on the configuration of the circuit. If Q2 is being turned on by the low state of A or B, Q1 does not receive the necessary bias to turn it on, thus remaining in the off state. This type of transistor behavior is crucial for implementing logic functions in electronic circuits.

In summary, when either A or B is low, the circuit design ensures that Q1 is off, preventing it from saturating, while Q2 turns on, allowing current to pass through.