Waves

Are the transfer of energy from one place to another without the net displacement of matter.
- Mechanical Waves have an absolute requirement for a medium e.g. Sound cannot propogate through a vacuum
- Non-Mechanical Waves (EMR) - does not require a medium, can propogate through a vacuum but can also propogate through other media - e.g light
The direction of displacement of particles in the media
- Transverse waves - perpendicular to the direction of propogation
- Longitudinal waves - parallel to the direction of propogation
Below, Amplitude (A) is the max displacement of a particle in the medium from the mean/ medium position (x-axis). For a displacement-distance graph, the time between two consecutive in phase points gives the wavelength of the wave. Period (T) is the time it takes for a single wave to pass a given point. Wavelength is the distance between two consecutive in-phase points.
Frequency cannot be directly gotten from a wave graph $\downarrow$, $T=\dfrac{1}{f}$
- *FREQUENCY is a fundamental property of the wave that CANNOT change.
$V=\lambda f=\dfrac{\lambda}{T}$ where $x$ is speed in $m\space s^{-1}$, $\lambda$ is wavelength in metres, and $T$ is period in seconds, and $f$ is the frequency in $s^{-1}, Hz$

Wave Behaviours

Reflection - when energy is incident upon a surface, or a boundry between two different media, then some/all of the energy rebounds back into the original medium.
Wavelength and speed will remain constant if there is a reflection. Frequency is always constant
The law of reflection states that the angle of reflection is equal to the angle of incidence.

The reflection of sound from a hard surface.
How long before hearing sound/how long before it hits the wall are the questions that will be asked
- Need to consider speed of sound in air at $25\degree$ as $346m s^{-1}$ (its on the data sheet)
- Knowing the distance from the wall, we can figure out how long to get to wall ($\frac{s}{v}$) and how long to hear the echo ($2\frac{s}{v}$)

When a wave enters a new medium at an angle other than $90\degree$, then it will change direction
Velocity ($v$) changes
- Since $f$ cannot change, then to change $v$, $\lambda$ must change (wavelength will change)
Light decreases in speed with increasing density of the medium
Sound increases in speed with increasing density of the medium
If entering a FASTER medium, then the refracted ray bends away from the normal, and if entering a SLOWER medium, the refracter bay bends towards the normal
- The normal is the perpendicular line that can be made with the surface (this is why the wave does not change direction if it enters perpendicular to the medium)

Radiate: Point source emitting things
Occurs when waves either pass through a gap or around an obstacle and the wave fronts are deformed (bend). IF $\lambda \geq d$ where $\lambda$ = wavelength and $d=$ size of gap
If two crests meet, they constructively interfere to form a crest with an amplitude which is the sum of both amplitude

On the data sheet, it is a relationship
- $I=\frac{P}{A}$ where the units are $W m^{-2}$ or, more familiarly, the logarithmic $dB$ scale.
The model assumes no loss in energy
- The reason $A$ decreases is because the power is being spread about a larger area; if $A$ stayed the same, there would be an **INFINITE ENERGY GLITCH