Where do variations in input signal polarities occur in a Class A amplifier?

Variations in input signal polarities in a Class A amplifier occur throughout the entire signal cycle. This means that both positive and negative halves of the input signal can lead to corresponding variations in the output due to the design and operation of the Class A amplifier.

In a Class A amplifier, the transistor is biased in such a way that it remains in an active conducting state for the entire input signal cycle. As the input signal oscillates, the output reflects these variations in polarity, effectively amplifying both the positive and negative excursions of the input. This contrasts with other classes of amplifiers where such behavior may be constrained to specific regions of operation.

Choosing the first option highlights the complete range of operation where these variations can occur. The cutoff limits and saturation do play a role in determining the overall efficiency and linearity of the amplification, but the key characteristic of Class A amplifiers is the continuous conduction behavior across the full cycle of the input signal. This continuous conduction allows for a faithful reproduction of the input signal's amplitude and polarity variations, which is critical for high-fidelity audio amplification and other applications where signal integrity is paramount.