# Waves Unit

The direction of motion of the particles compared to the direction of the wave motion determines whether the wave is transverse or longitudinal. Write the definitions of these waves down in your notes.

A wave is a disturbance that travels from one place to another and transfers energy.

An oscillation means moving back and forth at a regular rate.

1 wave is one full part of a wave that keeps repeating.

The medium is the material the wave moves through (or the material that is moving).

Transverse waves move perpendicular to the direction of the particle motion.

Longitudinal waves move parallel to the direction of the particle motion.

1.  Notice in the picture above that longitudinal waves also have wavelengths

2.  In your notes, make sure you can identify crests, troughs, amplitudes, and wavelength for a wave.

Sketch this diagram in your notes:

Sketch this diagram in your notes:

Expansions are sometimes called rarefactions

For longitudinal waves, the wavelength is measured from compression to next compression or expansion to next expansion.

4/8/24

• The definition of frequency is how many times a point on a wave oscillates (back and forth)

• Mechanical waves can only travel through a medium. In other words, mechanical waves need atoms/molecules to transfer energy.

• The particles (atoms/molecules) only oscillate; they do not move with the wave!!

• Electromagnetic waves are made of oscillating electric and magnetic fields and do not require a medium.

• Memorize these electromagnetic waves in order:

• Examples of mnemonic devices to memorize electromagnetic waves:

• Raging Martians Invade Venus Using X-ray Guns

• Rabbits Mate In Very Unusually Xpensive Gardens

• ROYGBV: Red, Orange, Yellow, Green, Blue, Violet

• Waves can be transverse or longitudinal and mechanical or electromagnetic. There are no longitudinal, electromagnetic waves.

• Mechanical waves travel fastest through solids because the atoms/molecules are closer together.

• 1 cycle is one repetition of a wave's particle.

• Frequency (variable: f) is how many times (cycles) a point on a wave oscillates.

• Frequency is measured in units of hertz (Hz) or number of times per second (or other units of time).

• The period (variable: T) of a wave is the amount of time it takes for a point on the wave to oscillate once.

• The units of period are seconds.

• Relationship between period and frequency:

• T=1f or f=1T

• If the frequency is high, the period is small.

• If the period is large, the frequency is low.

4/10/24

• Frequency and amplitude do not affect the speed of a wave!

• Waves always travel at the same speed (or velocity) unless the medium/material changes!!!!!!!!!!

• This is true for mechanical and electromagnetic waves.

• Examples of changing the medium: changing the air temperature for sound, tightening/loosening a guitar string.

• The speed relationship for waves:

• v = λf

• v = velocity or speed (units: meters per second, m/s)

• λ = wavelength (units: meters, m)

• f = frequency (units: hertz, Hz)

• If the medium doesn't change, the wave speed stays the same, but the frequency and wavelength will change inversely with each other.

• If the medium changes, the wave speed changes, but the frequency stays constant.

• The speed of all electromagnetic waves (including light) in a vacuum is

• c = 3.0 x 108 m/s (300,000,000 m/s)

4/22/24

1. Reflection means waves are bouncing off the edge/end of a medium (boundary) back into that medium.

2. Reflection happens for all waves.

1. The normal is the imaginary line "perpendicular" to a surface.

2. The incident wave (or ray) is the original wave that moves towards the boundary.

3. The reflected wave (or ray) is the wave that bounces back into the original medium.

4. The angle of incidence and angle of reflection are measured from the normal

4/24/24

1. Interference is the combining of two or more waves when they occupy the same space together.

2. When waves undergo interference, they do not disappear. They combine together temporarily; then the individual waves continue in their original directions.

3. To determine the amplitude of the combined wave, simply add the heights of the individual waves at each point that they overlap.

4. Be sure to consider whether the amplitudes are positive or negative!!!

5. Constructive interference occurs when waves combine to create a larger amplitude (positive or negative).

6. Destructive interference occurs when waves combine to create a smaller amplitude (positive or negative).

7. The fact that light experiences interference provides evidence that light acts as a wave.

1. Resonance is the phenomenon where objects oscillate with increasing amplitude when stimulated with vibrations of a specific frequency (resonant frequency) that is specific to that object.

2. Resonance only happens with waves (not particles)!

5/3/24

• Diffraction is the process of waves bending around objects.

• Diffraction provides evidence that light acts as a wave.