The output of a Class B amplifier is present for what portion of the input cycle?

In a Class B amplifier, the output is active for half of the input signal cycle, or 180 degrees. This design utilizes two transistors, each conducting for one half of the waveform. One transistor handles the positive half of the cycle, and the other manages the negative half, effectively allowing the amplifier to produce a complete output while significantly reducing power loss and improving efficiency compared to Class A designs, which conduct for the entire cycle.

The reason why 360 degrees, less than 180 degrees, or more than 180 degrees do not apply is that those options suggest that the amplifier can output during the entire cycle, during a portion that doesn't represent the effective output of both halves, or exceed its operational limits, which is not characteristic of Class B operation. Thus, only being active for 180 degrees accurately reflects how a Class B amplifier operates within its design principles.