PS 1-7-08

Finish Light

Color

Uses of Electromagnetic spectrum

Properties of Sound

• How Fast

• Intensity

• Pitch

• Range of sound waves– Infrasound– Ultrasound

Use of Sound waves

• Echolocation

• Sonar

• Ultrasound imaging– Sonograms

Example of Ultrasonic sound waves

• 1 to 15 million Hz• Passes through most

materials, but reflects at medium boundaries

• Not harmful like x-rays

Used more frequently for other purposes

                                  

    

Why use ultrasonic waves?

• Focused into more narrow beams

• Directed more easily

SONAR

• Sound, Navigation, and RAnging

• Uses acoustic signals and echo returns to locate objects

• Ultrasound waves generally used

Sonar

Homework

Pg 498

Problems 1-5 and #9

Does light move as particles or waves?

Light produces interference patterns like water waves

Light can be modeled as a wave

• Transverse waves

• Electromagnetic wave (no medium, consist of changing electric and magnetic fields)

• Reflection, refraction, or diffraction

• Interference, produce standing waves

Wave model can not explain some observations

• Some frequencies of light can knock off electrons from a metal plate upon impact

• Some light waves with more energy can not.

• Dim Blue light does, Bright red does not

Light can be modeled as a stream of “particles”

• These particles are called photons

• Do not have mass

• Packets of energy

• Unlike a wave, located in a particular place

• Also can be used with reflection, refraction

Scientist have not determined if light is only a wave or particle

They currently accept either models, depending on the

situation

Energy and Frequency

• The energy of light is proportional to frequency

• Higher frequency more energy

• Blue light has more energy than red light

Speed of light

• Depends on medium

• C = speed of light = 3 x 108 m/s in nothing

• Slows down as the density of material increase

• Visualized by the bending of light (refraction)

Brightness of light

• measured by objects Luminosity

• # of photons or wave-fronts passing through a certain area of space

• Luminosity decreases proportionally with distance

Homework on page 498

Question 1: Identify 2 factors that may affect the speed of sound.

Answer: type of medium, temperature

Homework

Question 2: Explain why sound travels faster in water than air

Answer: In air, molecules are far apart, collide less often

Homework

Question #3: Distinguish between infrasound and ultrasound

Answer: Infrasound are sound waves with a frequency under 20 Hz. Ultrasound are sound waves greater than 20,000 hz.

Homework

Question #4: Determine which of the following must change when the pitch gets higher

Answer: Frequency increases, wavelength decreases

Homework

Question #5, Determine which of the following must change when the sound gets louder

Answer: a,d Amplitude and intensity increase because there is more energy in the sound wave

Homework

Question #9: Why are sonograms made with ultrasound waves instead of audible sound waves?

Answer: Ultrasound waves pass easily through tissue, audible sound waves do not

Quiz question

• Determine which of the following must change when the pitch gets higher?

a) intensity

b) wavelength

c) speed of the wave

d) amplitude

e) frequency

From Friday

• Evidence that light travels as a series of waves

• Evidence that light travels as a stream of particles

• What is a photon?

• How does the amount of energy carried by a light wave relate to its frequency?

Connections between light and sound

• Both light and sound can vary in intensity

light-brightness

sound-loudness

• Both can vary in speed by change of medium– Light slows down with more dense mediums– Sound speed up with more dense mediums

Goals for Today

• Discuss the electromagnetic spectrum in more detail

• Determine why you see things as a certain color

Electromagnetic Spectrum

• Visible light make up just a small part of the range of light waves, just like audible sound.

• Electromagnetic spectrum consists of light at all possible energies, frequencies and wavelengths

Similarities between different parts of the spectrum

• All move at the same speed through a given material

• All do not need a medium to move

• All are transverse waves

Differences in the spectrum

• Different waves have different wavelengths and frequencies

• Different frequencies carry different amount of energy

• Larger frequency, larger amount of energy

Regions of the spectrum

• Gamma and x-rays have the largest frequency (therefore, smallest wavelength)

• Small enough to pass through most parts of body without meeting anything

• In x-rays, those that hit bone are absorbed, and do not hit the photographic plate (dark and light parts)

X-ray image

The good and bad of gamma and x-rays

• High energy

• Interaction may kill living cells or alter them to produce cancerous cells

• Can also be used to kill cancerous cells

a form of “ radiation therapy”

Radiation Therapy

Ultraviolet light

• Smaller frequencies than x-rays but more than visible light

• This is the portion of light spectrum that causes sunburn, even on cloudy days

Sunbathers

Infrared light

• Frequencies of light slightly smaller than visible light

• All matter warmer than absolute zero gives out infrared or “radiant heat”

• Can be sensed by some living beings

• Infrared cameras, heat seeking missiles

Infrared uses

Microwaves and Radio waves

• Microwave, Radio and TV waves are the largest in wavelength, smallest in frequency

• Boundary between types is arbitrary

Microwaves

• Microwaves are

reflected by metals

pass thru air, glass, paper plastic

absorbed by fat, water and sugar

Energy of wave passes into food, makes molecules vibrate- heat up

Uses of microwaves

Mobile phones

Use microwaves to transmit information

Least effected by surroundings

Homework

• Pg 505

• Problems 1-5

Colors that you see

• Different wavelengths (and frequencies) correspond to different colors of light

• An object that reflects a certain wavelength of light has that color

• If multiple wavelengths of light are reflected, secondary colors are created

• For light

• If all visible wavelengths of light are combined in sunlight

• Humans detect yellow-green the easiest

• Black is the absence of reflected light

• Mixing all three primary colors produces white light

Certain colors absorbed in water

Color of plants on other planets