The correct answer is D. Newton
<span>sound waves are a type of wave sometimes called compression waves, vibrations with enough of an amplitude can compress and decompress the air adjacent to the object causing the waves to form.</span>
Get a pull chord light switch installed in her bathroom by a qualified electrician asap. Meanwhile, keep hands as dry as possible, and try not to go near that switch until it's either been properly earthed, or whatever the problem actually is, and get qualified advice on what the problem is. Don't have wet feet either, and don't stand in puddles of water whilst operating - i she has to - the switch. 250V AC mains can be lethal, and at least painful.
To solve this problem it is necessary to apply the concepts related to the principle of superposition and constructive interference, that is to say everything that refers to an overlap of two or more equal frequency waves, which when interfering create a new pattern of waves of greater intensity (amplitude) whose cusp is the antinode.
Mathematically its definition can be given as:

Where
d = Width of the slit
Angle between the beam and the source
m = Order (any integer) which represent the number of repetition of the spectrum, at this case 1 (maximum respect the wavelength)
Since the point of the theta angle for which the diffraction becomes maximum will be when it is worth one then we have to:


Applying the given relation of frequency, speed and wavelength then we will have that the frequency would be:

Here the velocity is equal to the speed of light and the wavelength to the value previously found.


Therefore the smallest microwave frequency for which only the central maximum occurs is 1.5Ghz