Answer:
The low points are called troughs
The particles are either being absorbed or evaporating
Answer:within the focal length of the lens, provided the focal length is shorter than the near point distance.
Explanation:Hope it helps
The basic relationship between the frequency of a wave and its period is

where f is the frequency and T the period of vibration.
In our problem, the frequency is

so, by re-arranging the previous formula, we can find the period of the wave: