The story is open to interpretation, but a common view is this. The pit represents hell or death, because it is a frightening, unknown concept to the narrator. The pendulumrepresents time. It swings like a clock pendulum, which shows the seconds until the next minute. Each swing for this bladed pendulum means one step closer to death. The rats (although commonly viewed as vulgar, unwanted creatures, which is what the narrator thinks at first) can prove to be a second chance at life. The rats chew through the bindings on the narrator, freeing him and escaping the pendulum. The narrator is using something viewed as bad to his advantage. Also, the narrator's rescue can also be viewed as a second chance, or "heaven" opposed to the hellish pit.
Basically, Poe's message was a simple one. In life, people can take a bad situation and use it to their advantage.
2. Transverse waves
Light waves HAVE radiant energy.
Amplitude and wavelength are independent variables.