Question

if the number of throughs that pass a point in a given time increases, what has decreased

Answer 1

The number of throughs (and crests) that pass a point in a given time gives the frequency of the wave. In fact, the frequency is exactly defined as the number of complete cycles of a wave that pass a given point in a given time. Therefore, if the number of throughs that pass a point in a given time increases, the frequency of the wave increases as well. But the frequency is the reciprocal of the period:
$f= \frac{1}{T}$
where T is the period. The two quantities are inversely proportional to each other, therefore since the frequency has increased, the period of the wave has decreased.

Answer 2

Answer:

Time period and wavelength decreases

Explanation:

The number of troughs or number of crest is called the frequency of wave. The relation between the frequency and the time period is inverse. Mathematically, it can be written as :

$f=\dfrac{1}{T}$

So, if the number of troughs that pass a point in a given time increases, then the time period of the wave decreases.

Similarly, on increasing the number of troughs or the frequency of the wave, the wavelength also decreases. This is because the relationship between the frequency and the wavelength is inverse i.e. v = υ × λ.