Answer to Question 1
With demand characteristics, the participants react to the perceived demands of the situation, that is, what they think the experimenter expects of them. As such, they don't act naturally. Instead, they respond to clues in the environment to direct their behaviors.
Evaluation apprehension affects participants as they act differently because they know they are being observed. They may act in a particular way in order to look better in the eyes of the researcher, for instance.
Answer to Question 2
The Hawthorne effect refers to the phenomenon in which a research participant acts differently in order to meet the perceived demands of the situation. It is a poor term to describe how people react to the expectations of an experimenter because in the original Hawthorne studies, the workers' behaviors didn't change due to demand characteristics but to other extraneous influences.
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