WAVE Basics Chapters 15

What are Waves? A wave is a disturbance that transmits energy through matter or space.

Types of Waves There are two types of waves: Mechanical: Require a medium (matter through which a wave travels) Examples Include: Ocean waves, medium = water Sound waves, medium = air Seismic Waves (Earthquake), medium = earth

Types of Waves Electromagnetic: caused by a disturbance in electric and magnetic fields and do not require a medium. Examples include:

Wave Movement A wave front is the front of a wave that is transferring energy. In a single system all of the wave fronts have the same amount of energy, but as the wave front spreads out, so does the energy.

Wave Movement Waves can move in two basic ways: Transverse Motion: particles of the medium vibrate perpendicularly to the direction the wave travels. Example: light wave Longitudinal (Compressional) Motion: particles of the medium vibrate parallel to the direction the wave travels. Example: sound wave

Parts of a Wave You will be responsible for identifying parts of a wave on both a transverse and longitudinal wave. Complete the descriptions and label the following on your note outline:

Parts of a Wave Transverse Wave: The top of the wave is called a crest (peak); the bottom of the wave is called the trough. Longitudinal Wave: The point of maximum compression is called a compression; The point of least amount of compression is called a rarefaction. Crest Trough Compression Rarefaction

Parts of a Wave Wavelength (λ) is the total length of 1 wave. In transverse waves it’s typically measured from crest to crest or trough to trough. In longitudinal waves it’s measured from compression to compression or rarefaction to rarefaction. The shorter the wavelength, the more energy the wave is carrying. 1 λ 1 λ 1 λ 1 λ

Parts of a Wave Amplitude can be measured on a transverse wave. It height from the resting point to the crest or the resting point to the trough. The larger the amplitude, the more energy the wave is carrying. Amplitude Amplitude

Wave Measurements A period (T) is the time it takes for one full wavelength of wave to pass a certain point. A period is a measurement of time, so its SI unit is seconds (s).

Wave Measurements The frequency (f) of a wave is the number of full wavelengths that pass a given point per second. The SI unit for measuring frequency is Hertz (Hz).

Wave Measurements The frequency (f) of a wave is the number of full wavelengths that pass a given point per second. The SI unit for measuring frequency is Hertz (Hz). Frequency is the inverse of period f = 1 / T

wave speed (m/s) = frequency (Hz) x wavelength (m) Wave Measurements Wave speed (v) is the speed at which a wave passes through a medium and is measured using the following equation: wave speed (m/s) = frequency (Hz) x wavelength (m) v = f x λ

Wave Measurements A wave along a guitar string has a frequency of 440 Hz and a wavelength of 1.5 m. What is the speed of the wave? v = ? m/s f = 440 Hz λ = 1.5 m v = f * λ v f * λ v = 440 Hz x 1.5 m v = 660 m/s

Wave Measurements The speed of sound in air is about 340 m/s. What is the wavelength of sound waves produced by guitar strings vibrating at a frequency of 440 Hz? v = 340 m/s f = 440 Hz λ = ? m λ = v / f v f * λ λ = 340 m/s / 440 Hz λ = 0.77 m

Wave Measurements The speed of light is 3 x 108 m/s. What is the frequency of microwaves with a wavelength of 0.01 m? v = 3 x 108 m/s 300,000,000 m/s f = ? Hz λ = 0.01 m f = v / λ v f * λ f = 300,000,000 m/s / 0.01 m f = 30,000,000,000 Hz

Wave Behavior A reflection is the bouncing back of a wave as it meets a surface or a boundary.

Wave Behavior How a wave reflects depends upon the surface that it bounces off of. Example: When sending pulses down a rope with a free end, the wave comes back normal. Example: When sending pulses down a rope with a fixed end, the wave comes back inverted. Free Fixed

Wave Behavior Diffraction is the bending of a wave as it passes an edge or an opening.

Wave Behavior Refraction is the bending of waves as they pass from one medium to another.

Wave Behavior Interference occurs when the combination of two or more waves exist in the same place at the same time. Constructive interference = bigger wave. Destructive interference = smaller wave.

Wave Behavior Standing waves are caused by two identical waves going in opposite directions. Series of constructive and destructive interferences. They have regions of no vibration (nodes) and regions of maximum vibration (antinodes).

Wave Behavior The frequency of a wave can change when the source of the wave or the observer is moving. This is called the Doppler Effect.