Types of Waves and Wave Properties | MCAT Physics Prep

Need help preparing for the Physics section of the MCAT? MedSchoolCoach expert, Ken Tao, will teach everything you need to know about Types of Waves and Wave Properties. Watch this video to get all the MCAT study tips you need to do well on this section of the exam!
A wave is a disturbance that transfers energy through matter or space. Essentially, a wave can be thought of as moving energy. When you think of a wave, you're usually thinking about objects oscillating up and down. In some cases, the oscillations occur in a physical medium such as water, where waves are moving up and down. On the MCAT we primarily classify waves as transverse waves or longitudinal waves. The main difference between the two types of waves is the direction of their oscillations relative to their direction of propagation.
Transverse Waves
The oscillations of transverse waves are perpendicular to the direction of wave propagation. In one example, the wave is moving from left to right, but molecules seem to be oscillating up and down the page. Light is an example of a transverse wave with two components: an electric field and magnetic field. Both fields are propagating in the same direction, but each field oscillates in a direction perpendicular to their propagation and perpendicular to one other.
Longitudinal Waves
Longitudinal waves have oscillations that are parallel to the direction of wave propagation. The diagram below depicts the wave as traveling in a horizontal direction, where particles experience compression and rarefaction. In areas of the wave where particles are compressing, there’s a high density of particles. In areas where the particles have spread out (rarefacted), there is a low density of particles. The oscillation of particles between areas of high and low density occurs in the direction of wave propagation, which is what defines something as a longitudinal wave.
Properties of Waves
In order to characterize waves, we need to discuss several key properties of any given wave:
- The propagation speed of a wave is the distance traveled by the wave per unit time. The propagation speed of light is a constant value you should know for the MCAT: 3 x 108 m/s.
- The amplitude of a wave is the maximum displacement it has away from its origin on the axis which it oscillates across. The amplitude of the electromagnetic wave would be the wave’s maximum height in the vertical direction. The amplitude of a wave is important in determining the energy of a wave, because the energy contained by a wave is directly proportional to the amplitude of the wave squared. A wave with greater amplitude has much more energy.
- The cycle of a wave is the process by which a wave moves from one point and returns to the same point. For instance, starting at a peak on an electromagnetic wave, one cycle will have occurred when it reaches the next peak on the wave.
- The wavelength of a wave is the distance traveled in one cycle.
- One period is the amount of time taken to complete one cycle.
- Frequency is the number of cycles a wave completes per second (with units of 1/s, s-1, or Hz).
- Phase is the initial position of a wave along its cycle.
- The phase difference of a wave compares the phase of two waves. If the two waves can be lined up perfectly, they are “in” phase. When two waves are perfectly in phase, they experience constructive interference. When two waves constructively interfere with one another, their amplitudes are combined to give a total greater amplitude, increasing the net wave energy. Conversely, if the crests of one wave align with the troughs of another, the waves are perfectly out of phase. When two waves are out of phase, they experience destructive interference, in which the reverse occurs: their amplitudes are diminished, and net energy is decreased.
Traveling one cycle around a circle is 360 degrees, so we can use 360 degrees to represent the cycle of a wave. If two waves are 0 degrees apart, they are in phase, and if they are 360 degrees apart they are also in phase, because they are one full cycle apart. Being one full cycle apart, the crests and troughs of the waves will still align and the waves will yet experience constructive interference. If the two waves are 180 degrees apart, they are half a cycle apart. In that case, the troughs of one wave will overlap with the crests of the other wave, so they are fully out of phase and will only experience destructive interference. If they experience only destructive interference, the two waves will completely cancel each other out.
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[@JasonVaysberg]

I would love the subsequent videos on light and sound :D These videos are super helpful!

[@user-bj5zk8pz8f]

Thank you for this!! Where's the video on light and sound?

[@dylonmayer3520]

Your videos are awesome. Thank you for making them!

[@matthewmorris130]

In transverse waves like water, how does vertical movement of particles translate to horizontal movement of the wave?