The wave speed completely depends on the characteristics and properties of the medium . . . physical properties for mechanical waves, electrical properties for electromagnedtic waves.
So if you want to change the speed of a wave, you have to change the medium . . . shoot it through some different kind of stuff. <em>(B) </em>
Answer:
Reactance
Explanation:
In an AC circuit, the capacitive reactance of a capacitor is given by:

where
f is the frequency of the AC current
C is the capacitance of the capacitor
The reactance of the capacitor tells somehow the "resistance" of the capacitor to the passage of current through it. In fact:
- When the frequency of the AC current is zero (this means, we are in regime of DC current), the reactance becomes infinite, and this is true because the capacitor does not let the current pass through it)
- When the frequency of the AC current tends to infinite, the reactance becomes zero, and this is true because in this case the current changes direction so fast that the capacitor has not enough time to "block" the current, so the current almost no feels the presence of the capacitor.
Risks are only in a persons