PROPERTIES OF WAVES Let’s Surf!
What is a wave? A wave is an oscillation that travels, moving energy from one place to another Caused by a vibration The oscillation spreads outward from where it started.
Properties of a Wave A crest is the highest point of the wave. A trough is the lowest point of the wave.
Properties of a Wave The amplitude, A, of a wave is the maximum height the wave rises above the origin (equilibrium point).
Properties of a Wave The wave period, P, is the time it takes one wave to pass the observer.
Properties of a Wave Wavelength is the distance from any point on a wave to the same point on the next cycle of the wave (usually from crest to crest). Symbol: Units: meters (m)
Properties of a Wave The frequency of a wave is the number of waves passing a particular point in one second. Symbol: ƒ Unit: Hertz (Hz) or s -1
Speed of a Wave The speed is the distance traveled (one wavelength) divided by the time it takes (one period). Speed = frequency X wavelength v = ƒ·
Example Calculations: The wavelength of a wave on a string is 1.5 meters and its speed is 5 m/s. Calculate the frequency.
Review Problems 1. What is the speed of a wave with a frequency of 22 Hz and a wavelength of 6.2 m? 2. Calculate the frequency of a wave traveling at 3.0 x10 8 m/s with a wavelength of 1.96 x m.
Relationship between frequency, wavelength and energy: There is an inverse relationship between wavelength and frequency. There is a direct relationship between energy and frequency. Therefore: As wavelength increases, both the frequency and energy of the wave decrease. As wavelength decreases, both the frequency and energy of the wave increases.
What is a wave “pulse”? A wave pulse is a short ‘burst’ of a traveling wave. It is sometimes easier to see the motion of wave pulses than it is to see long waves with many oscillations.
Types of Waves: Transverse A wave whose oscillations are perpendicular to the direction the wave travels. Examples: Water waves, light waves, S- waves
Types of Waves: Longitudinal A wave whose oscillations are in the same direction as the wave travels. aka = compression waves Examples: Sound waves, P-waves
Standing Waves: A wave trapped in one spot. Ex. Guitar string
Four wave interactions When a wave encounters a surface, four interactions can occur: 1. reflection 2. refraction 3. diffraction 4. absorption
Examples of Interactions: 1. Reflection: Mirror (light), echo (sound) 2. Refraction: Eyeglasses, microscope lenses 3. Diffraction: Hologram, prism 4. Absorption: Sunglasses absorbing UV radiation Sound proofing a recording studio We see colors due to both absorption and reflection!
Constructive Interference: Constructive interference happens when waves add up to make a larger amplitude. Suppose you make two wave pulses on a stretched string. One comes from the left and the other comes from the right. When the waves meet, they combine to make a single large pulse.
Destructive Inference During destructive interference, waves add up to make a wave with smaller or zero amplitude. What happens when one pulse is on top of the string and the other is on the bottom? When the pulses meet in the middle, they cancel each other out.