# Wave Basics Unit 9 – Lecture 1.

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Wave Basics Unit 9 – Lecture 1

Waves rhythmic disturbances which transmit energy
through a medium [substance – solid, liquid, or gas] ex: light & sound [note: sound and other types of waves can carry information in the form of energy]

Waves Cord Demo – does the cord itself move from place to place? is it traveling with the wave? Waves move through the medium – they do not move the medium itself. like the wave at a sporting event

Types of Waves Mechanical waves – need to travel through matter
transverse waves compressional [aka longitudinal] Water waves move in a combination of these movements

Transverse Waves Transverse waves
matter in medium moves back and forth at right angles to the wave’s energy Electromagnetic rays travel in transverse waves if wave is traveling L or R, the movement of the medium is up and down. if wave is traveling up or down, the movement of the medium is L & R

Transverse Waves Parts of a Transverse Wave
draw this wave on your paper in the space provided.

Transverse Waves Parts of a Transverse Wave crest
the highest point of the wave – highest E there can be many crests

Transverse Waves Parts of a Transverse Wave trough
the lowest point of the wave – lowest E there can be many troughs

Transverse Waves Parts of a Transverse Wave resting position
does not have to be at zero!

Transverse Waves Parts of a Transverse Wave amplitude
the furthest distance from the resting position from resting position to either crest or trough

Transverse Waves Parts of a Transverse Wave wavelength
distance of one wave distance between two equal points on a wave

Transverse Waves

Longitudinal Waves Longitudinal Wave [aka Compressional Wave]
matter in the medium moves back and forth along the same direction of the wave sound and seismic waves imagine a coil: a slinky or spring compress coils then release, wave moves coils in a compression to other side

Longitudinal Waves Parts of a Longitudinal Wave
Draw a coil on your sheet like the one below, with areas of densely bound coils, and areas of lesser bound coils

Longitudinal Waves Parts of a Longitudinal Wave rarefaction
a non-compressed area of this type of wave point of lowest energy

Longitudinal Waves Parts of a Longitudinal Wave compression
a compressed area of this type of wave point of highest energy

Longitudinal Waves Parts of a Longitudinal Wave wavelength
distance of one wave distance between two equal points on a wave

Longitudinal Waves

Transverse vs Compressional Waves
Transverse waves Longitudinal Wave [aka Compressional Wave]

Practice What is a wave? What is the name for the material through which a wave travels? In which kind of wave do the particles of the medium vibrate in the same direction as the wave? What is transmitted by a wave? In which kind of wave do the particles of the medium vibrate at right angles to the wave? How is a crest similar to a compression / a trough similar to a rarefaction?

Wave Measurements Frequency – number of waves that pass a certain point per unit of time. [waves per time] measured in Hertz [Hz] for waves per second as waves travel faster [higher frequency], the wavelength decreases what type of relationship is this? 1 Hz = 1 wave per second

Wave Measurements Period = time it takes to complete one cycle [time per wave] T = t / # of waves OR this is the inverse of frequency T = 1/ f

Practice The period of a wave is 3 seconds. What is its frequency?

Wave Measurements Wave Speed can depend on the medium
sound travels best through solids [particles close together] but radio waves and others can’t travel through them

Wave Measurements Calculating Wave Speed
recall: speed = distance / time recall: frequency = waves/time wave speed = wavelength * frequency v = λ * f does this make sense? let’s see wave speed (m/s) = wavelength (m) * waves (#) time (s)

Electromagnetic Waves
Electromagnetic Waves – do not need matter to transfer energy wave transferred by vibration of magnetic & electric fields EMS = range of electromagnetic radiation EMS contains Visible Light in roughly the center of spectrum R O Y G B I V

Electromagnetic Waves
all EM waves travel at the speed of light roughly 3 x 108 m/s or 186,282.6 miles per second variable for speed of light = C this is currently the fastest speed in the universe

Electromagnetic Spectrum

Electromagnetic Spectrum
How to remember?

Electromagnetic Spectrum
Helpful Prefixes: mega = M = 1 x 106 nano = n = 1 x 10-9