Waves
What are waves?
Before we delve into light and sound, you need some background knowledge on waves. A wave is a vibration in space and time, and a vibration is a side-to-side, up and down, or front and back movement. You can see vibrations when you pluck a guitar string. You can create a wave yourself. Take a slinky and move it up and down. The pattern you have created is a wave.
Waves have multiple parts. The highest point in a wave is known as its crest and the lowest point in a wave is known as its trough. The amplitude of a wave is the distance from its midpoint to one of its extremities (crests or troughs). The wavelength is the distance from the top of one extremity to the top of the next extremity.
The frequency of a wave is how frequently the wave vibrates. The unit of frequency is called the Hertz. 1 vibration per second is 1 Hz, which is pretty straightforward. A period of a wave is the time it takes for a complete vibration. A period is also a miserable time for all women. You get me girls. Frequency and period are inversely proportional. In other words, frequency = 1 / period and vice versa.
Waves don't necessarily travel at one speed. Unlike you on the highway. Wave speed depends on the frequency and wave length of the wave. Wave speed = frequency x wavelength
Transverse and Longitudinal Waves
There are 2 kinds of waves - transverse and longitudinal. Revisiting the slinky (I like slinkies), a longitudinal wave is a wave in which the direction of travel is the same as the direction of the vibration. A transverse wave is a wave in which the direction of travel is perpendicular to its direction of vibration.
Longitudinal waves have compressions (areas where parts of the slinky are compressed) and rarefactions (areas where parts of the slinky are stretched apart), as you can see in the image below.
Interference
Interference happens when two waves encounter each other. Let's use transverse waves for our example:
If the crests and troughs of transverse waves align, their amplitudes add together. This is constructive interference. When the crest of one wave aligns with the trough of the other, their amplitudes cancel each other out. This is destructive interference. Interference occurs with longitudinal and transverse waves.
However, some waves dont align exactly. Their frequencies are only slightly different. In sound waves, this produces beats - fluctuations in the loudness of the noise. Some parts cancel each other out while others dont, creating these beats.
Standing Waves
Standing waves are also a crazy phenomenon. For example, if you take that slinky and put it against the wall, the wave travels along the slinky, hits the wall, and comes back - the wall is too rigid to vibrate. If you keep pushing against the slinky as the wave is traveling back, you produce a standing wave. The nodes of the wave are stationary while the antinodes (halfway between the nodes) experience the largest displacements.
Waves combine to form composite waves. Composite waves are combinations of other sine waves (geometric waveforms that ocillate, as I mentioned earlier. They are like the perfect waves, and they are transverse)
