WAVES Light and Sound Waves All waves carry

WAVES Light and Sound

Waves All waves carry energy by rhythmic disturbances (vibrations) • Mechanical - require a medium (air, water or any type of matter) for movement – Transverse – Longitudinal / compressional (ex: sound) • Electromagnetic - move through empty space (ex: light, radiation) These travel as transverse waves!!!

All waves have similar properties • Frequency- the number of vibrations per • • second (is related to the speed of the movement of the vibrating particles) Amplitude – the height of the wave (the size of the movement of the vibrating particles) Both are controlled by the disturbance that created the waves

Wave frequency is the amount of waves that move through a point per second and is measured in the units of Hertz (Hz). Point A The diagram above shows 3 waves going through point A in 1 second. The frequency would be 3 Hz.

Waves - 2 Types

Transverse Waves • In transverse waves particles • vibrate at right angles to the direction the wave travels. Ex. E. M. Waves, waves on a slinky or rope coil, ocean waves

Longitudinal Waves • Also called compressional waves • Vibrating particles move back and forth along • • the direction of the wave velocity Parts consist of compressions and rarefactions Ex. Sound Waves

But there are some waves that don’t travel through a medium… Microwaves Radio Larger Waves Infrared Visible X-Ray Ultraviolet Gamma Smaller Waves Electromagnetic waves such as visible light travel throughout “matter-less” space.

Radiant Energy or Electromagnetic Energy (EM) • All radiant energy travels at 3. 0 x 108 m/sec in • • space Velocity of a wave = wavelength x frequency Visible light is just one type of EM Energy

Electromagnetic Spectrum All of the forms of radiation are given off by vibrating electric charges. Radiation comes in the form of vibrating or “throbbing bundles of energy” called photons. The frequency of the vibrating electric charges determines which type and how much energy will be given off.

The entire E. M. Spectrum in order from lowest to highest frequency • Radio waves: AM and FM • Microwaves: cooking /communication • Infrared: heat • Visible: (ROYGBV) • Ultraviolet: tanning • Xrays: medical • Gamma:

Velocity of all waves v=f λ f-frequency and λ is wavelength (distance between identical points on two consecutive waves)

Calculating the Velocity of a Wave A wave moves through water. The length of the wave is 5 meters. The frequency is 2 waves per second (2 Hz). What is the velocity of the wave? v= xf V= ? =5 m f = 2 Hz xf 5 m x 2 Hz 10 m/s

And the answer is? J 3300 Hz At 0°C sound travels through air at a speed of 330 m/s. If a sound wave is produced with a wavelength of 0. 10 m, what is the wave’s frequency? F 0. 0033 Hz Use the formula chart!!! G 33 Hz Velocity = f λ OR H 330 Hz J 3300 Hz 330 m/s = f x 0. 10 m

Wave Interactions Reflection- bounce off barriers in regular ways The angle the wave hits the barrier is the angle it will leave the barrier. (Angle of Incidence = Angle of Reflection)

Wave Interactions Refraction- waves can change direction when speed changes as it enters a new medium

• When a wave is refracted through an object, it will ALWAYS bend TOWARDS the thicker part of the object.

Absorption • When a wave’s energy dies out in a material • Soft surfaces tend to absorb waves better than hard which reflect • Light waves get absorbed according to the color of the material – red absorbs all colors except for red light which is transmitted through

Wave Interactions - Diffraction – waves bend around obstacles – either through openings or around corners (this, along with reflection, is how we hear sounds around a corner)

Wave Interactions Polarization – the use of barriers to block certain waves. Light waves travel in all directions with both vertical and horizontal components. If you block the horizontal component, only the vertical component will continue.

Wave Interactions - Interference • When 2 waves interact because they are in the same spot at the same time • Constructive Interference – waves get bigger because crests overlap crests and troughs do same • Destructive Interference – waves get smaller because crests overlap troughs

Sound waves travel through a medium and can be visualized by compressional waves. As the sound moves through the medium, the particles vibrate against one another causing the compressions: A slinky is a good example of how compressional waves behave.

Sound acts like other waves • Echoes are reflected • • sound waves Sonar uses echoes to judge distance to obstructions Human hearing is 2020, 000 Hz, below 10 Hz is infrasonic, and above 20, 000 Hz is ultrasonic.

Depends on the frequency Higher note / Higher frequency Lower note / Lower frequency

Doppler Effect • caused by an object moving while emitting a sound wave or an object moving towards a wave source. – This causes an apparent increase in the pitch of the sound as the source gets closer and a drop in pitch as it gets further away. – This change in pitch is due to the apparent compression of the waves which results in an experienced increased frequency.

Resonance • Is the vibration of an object caused by being struck by a wave at a certain frequency

Sound Waves move through matter not through empty space. One tuning fork is struck and placed next to an identical fork. The two forks do not touch. The second tuning fork starts to vibrate because Resonance is the vibration of — of another object struck by a wave of the correct F interference frequency. Since the forks G the Doppler effect are identical, the second one receives the correct H resonance frequency to begin vibrating. J standing waves

Compressional Waves Compression Wavelength: Rarefaction Compression + Rarefaction

Medium (solid, liquid or gas) Temperature

Sound requires contact. Solid Liquid gas So which of the above would be a better medium?

Temperature Do molecules move faster or slower as temperature increases? So would sound travel faster or slower as temperature increases?

Light and lenses