WAVESMore Than Just a Trip to the

Beach

WAVES

• Waves – Any disturbance that transmits energy through matter or space.

• Waves are not matter, but move through it.

• Some waves travel through a medium and some don’t.

WAVES

• Medium (media) – A substance through which a wave can travel.

• A medium can be a solid, liquid or gas.• When a particle vibrates back & forth, it can pass

its energy to a particle next to it. As a result, the second particle will vibrate in a way similar to the first particle. Ex: sound and ocean waves.

• Mechanical Waves – Waves that need a medium to travel.

WAVES

• Electromagnetic Waves – These waves do not require a medium to vibrate.

• Examples: Visible Light, Sun Light, Microwave Ovens, TV & Radio Signals and X-rays

WAVES

• There are two types of waves based on the direction they travel.

• Transverse Waves – Particles vibrate with an UP and DOWN motion, perpendicular (at right angles) to the wave.

• Longitudinal Waves – Particles vibrate along the path that the wave travels.

WAVES

• Transverse Waves • A transverse wave’s particles vibrate

perpendicular to the direction the wave moves. Ex: wriggling a rope

• Crest – The highest point of a transverse wave.

• Trough – The lowest point between each crest.

WAVES• Longitudinal Waves

• You can create a longitudinal wave on a spring.• Compressions – A section of a longitudinal wave

where the particles are crowded together (similar to the crests of a transverse wave).

• Rarefactions – A section of a longitudinal wave where the particles are less crowded (Similar to the troughs of a transverse wave).

WAVES

• Mechanical waves (requiring a medium) can be either longitudinal or transverse.

• Example: Sound waves are longitudinal and Ocean waves are transverse.

• All electromagnetic waves (do not require a medium) are transverse waves.

WAVES

• Amplitude – Distance from the line of origin (center of the wave/equilibrium) to the crest of the wave.

• Amplitude indicates how much energy is being carried by the wave.

• small amplitude = low energy• LARGE amplitude = HIGH energy

WAVES

• Wavelength – Distance from one wave (usually a crest or trough) to the same point on the next wave.

• In general, a wave with a short wavelength carries more energy than a wave with a long wavelength.

WAVES

• Frequency – The number of waves passing a given point in one second.

• If the amplitudes are equal, high frequency waves carry more energy than low frequency waves.

• Hertz – 1 wave (or cycle) per second.• Humans can hear from 20 hertz to 20,000

hertz. Dogs can hear up to 35,000 hertz.

WAVES

• Wave Speed – The speed at which a wave travels.

• Wave Speed = Frequency x Wavelength• Wave speed changes based on the medium in

which it travels.• Sound travels through more dense material

faster than less dense material (sound travels through steel faster than air)

WAVE INTERACTIONS

• Waves move in a straight line and at a constant speed until they hit an object.

• Reflection – Wave reflecting back when hitting a barrier.

• Reflected sound waves = Echoes• Sound waves reflect best off smooth, hard

surfaces (compare gym vs. auditorium)

The Law of Reflection

• Reflection – When light or any other wave bounces off an object.

• The Law of Reflection – The angle of incidence is equal to the angle of reflection. Incidence is the falling of a beam of light on a surface.

WAVE INTERACTIONS

• Light waves reflecting off an object allow you to see that object.

• Refraction – The bending of a wave as it hits a medium.

• Speed of a wave depends on the medium in which it travels.

WAVE INTERACTIONS

• As a wave moves from one medium to another, the wave’s speed changes.

• This is why a pencil looks bent or broken when it is placed in a glass of water.

WAVE INTERACTIONS

• Diffraction – Waves bending around an object in its path.

• Sound diffracts more easily than light because sound waves have longer wavelengths compared to light waves.

• This is why you often hear voices from another room.

WAVE INTERACTIONS

• Interference – Two or more waves overlapping.

• Constructive Interference – Crests & troughs of multiple waves line up, increasing the energy and increasing the amplitude of the wave.

WAVE INTERACTIONS

• Destructive Interference – The crest of one wave lines up with a trough of another wave, causing the resulting wave to be smaller.

• Standing Wave – A wave forms a stationary pattern in which portions of the wave do not move and other portions move with a large amplitude.

WAVE INTERACTIONS

• Resonance – What occurs when an object vibrating at or near a resonant frequency of a second object causes the second object to vibrate.

• Ex: Tuning fork near string of a guitar will make the string vibrate and produce sound

SOUND

• Pitch – How high or low you perceive a sound.• The thicker strings of an instrument have a

lower pitch.• The pitch can be changed by pushing the

string against the neck of the instrument to change the strings length. Shorter strings vibrate at higher frequencies.

• Lower frequencies = lower pitch

SOUND

• Loudness – How loud or soft a sound is perceived to be.

• The harder you strike a drum, the more energy you have transferred to the drum.

• The drum moves with a larger vibration and transfers more energy to the surrounding air.

• The larger the amplitude = the louder the sound

SOUND

• Decibel (dB) – The most common unit used to express sound.

• Normal conversation = 60 dB

SOUND

• Echolocation – Process of using reflected sound waves to find objects.

• Beluga whales, bats and some species of birds use echolocation to hunt food & detect objects in their paths.

• SONAR (Sound navigation and ranging) – A range of electronic echolocation.

• Fisherman and ship navigators use SONAR.

SOUND• Ultrasonography (a type of echolocation) is used

in medical procedures.• A transducer produces ultrasonic waves, which

reflect off the patient’s internal organs or an unborn baby. These echoes are then converted into images that can been seen on a TV monitor.

• Ultrasound waves are safer than X-rays because sound waves are less harmful to human tissue.

ELECTROMAGNETIC WAVES

• All electromagnetic waves (radio, microwaves, sunlight, X-rays, etc) travel at the same speed in a vacuum – 300,000,000 m/s.

• The entire range of EM waves is called the electromagnetic spectrum.

ELECTROMAGNETIC WAVES

• In order of decreasing wavelength and increasing frequency:

• Radio Waves• Microwaves• Infrared Waves• Visible Light• Ultraviolet• X-rays • Gamma Rays

RADIO WAVES

• Radio waves have long wavelengths and low frequencies (thus low energy levels).

• Radio waves CANNOT be heard, but they carry energy that can be converted into sound.

• FM= Frequency Modulated• AM=Amplitude Modulated• AM waves travel faster than FM waves, but FM

waves carry more information thus their sound is better.

MICROWAVES

• Shorter wavelengths & higher frequencies than radio waves.

• The energy of microwaves cause water molecules inside food to vibrate. The vibration of the water molecules causes the temperature of the food to increase.

• Microwaves are also in RADAR. RADAR (Radio Detection and Ranging) is used to detect speed and location of objects.

INFRARED WAVES

• Infrared waves are emitted by the Sun.• They are absorbed by your skin when they

strike your body.• Infrared radiation is also emitted by objects

such as stars, planets, buildings, trees and people (the amount is dependent on the object’s temperature).

LIGHT

• Light is an electromagnetic wave (EM wave), thus it does not require a medium.

• An EM is produced by the vibration of an electrically charged particle.

• The emission of energy in the form of EM waves is called radiation.

LIGHT

• When electrons absorb energy, they temporarily jump to a new energy cloud. When it returns to its original position, the electron releases a small amount of energy called a photon.

LIGHT

• The speed of light is 300,000,000 m/s in space. (Light travels slightly slower in air, glass and other types of matter.)

• Light travels more than 880,000 times faster than sound.

• That is why you see lightning before you hear thunder even though they are produced at the same time.

VISIBLE LIGHT

Visible Light – The very narrow range of wavelengths and frequencies in the electromagnetic spectrum humans can see.

• Visible Light provides the energy necessary for photosynthesis.

• ROYGBIV• Based on decreasing wavelength and

increasing frequency

VISIBLE LIGHT

• Red – Longest wavelengths (least energy)• Violet – Shortest wavelengths (carries the

most energy of visible light waves)• When all the colors of visible light are

combined, you see the light as white light.• Sunlight, light from incandescent light, light

from fluorescent light bulbs are all examples of visible light.

ULTRAVIOLET LIGHT

• Produced by the Sun• UV light waves have shorter wavelengths and higher

frequencies than visible light (more energy)• UV lights kill bacteria on food and surgical

instruments• UV light helps your body to produce vitamin D• UV light can cause sunburn, skin cancer, wrinkles and

damages eyes

X-Rays

• Have a great deal of energy • Easily penetrate variety of material• Used to view bones. The X-ray waves will

penetrate skin and muscle, but are absorbed by bone.

GAMMA WAVES

• Very high energy• Used to treat cancer cells, but can kill normal

cells too

Light & Color

• White light is made of all the colors of light.

• Color is determined by the wavelength of the light wave (Red=longest, Violet=shortest).

Light & Color

• The color that an object appears to be is determined by the wavelengths of light that reach your eyes.

• Light reaches your eyes after being reflected off an object or after being transmitted through an object.

• After reaching your eyes, light is converted into electrical impulses and interpreted by your brain as colors.

Light & Color

• When white light strikes a colored opaque object, some colors of light are absorbed and some are reflected.

• Only the light that is reflected reaches your eyes and is detected.

• ….so, the colors of light that are reflected by an opaque object determine the color you see.

Light & Color

• Examples:

• When white light shines on a strawberry, only red light is reflected. All other colors are absorbed.

• What is being reflected when you see oranges?

Light & Color

• BLACK - A material that ABSORBS all wavelengths of visible light.

• WHITE - A material that REFLECTS all wavelengths of visible light.

LENSES

• Mirrors reflect light.• Lenses refract light.

• Mirrors and lenses are either concave or convex.

• Eyeglasses, binoculars, cameras, telescopes and movie projectors all use lenses.

Lenses

• CONVEX LENSES– Thicker in the middle than at the edges. They refract light TOWARD THE CENTER.

• CONCAVE LENSES – Thinner in the middle than at the edges. Light rays entering a concave lens is bent TOWARD THE EDGES of the lens.