Chapter 22—The Nature of Light Material on the Final Exam

Section 1—What is Light? Objectives How is light an electromagnetic wave? Explain how you could calculate distances traveled by light using the speed of light Explain why light from the sun is important

Light: An Electromagnetic Wave Light travels as a wave Light does not need matter to travel Light is an electromagnetic wave Electromagnetic waves are waves that consist of electric and magnetic fields that vibrate at right angles to each other

Electromagnetic Wave

Electric and Magnetic Fields An electric field surrounds every charged object A magnetic field surrounds every magnet

How EM Waves are Produced Produced by the vibration of an electrically charged particle Creates electric field Field starts vibrating Creates magnetic field Carries energy

The speed of light Fastest thing known to science In a vacuum 300,000,000 m/s 300,000 km/s Slows down in matter Faster than sound

The speed of light We can use the speed of light to find how far it travels Formula SI units for speed: m/s SI units for distance: m SI units for time: s Speed = distance time

Math Practice Math Practice You try! The distance from Earth to the moon is 384,000 km. Calculate the time it takes for light to travel that distance. You try! The distance from the sun to Venus is 108,000,000 km. Calculate the time it takes for light to travel that distance.

Math Practice Math Practice You try! It takes 2595 seconds (43 min) for light from the sun to reach Jupiter. How far away is Jupiter? You try! The alpha centauri system has two stars. If it takes 11470s for light to reach one star to the other, how far apart are they?

Light from the Sun Light is a major energy source for our planet Plants use it to make food Animals eat these plants Fossil fuels store solar energy from the past

Section 1—What is Light? Objectives How is light an electromagnetic wave? Explain how you could calculate distances traveled by light using the speed of light Explain why light from the sun is important

Section 2—The electromagnetic Spectrum Objectives Identify the two ways that EM waves differ from each other Describe some uses for radio waves and microwaves List examples of how infrared waves and visible light are important in your life Explain how ultraviolet light, X rays, and gamma rays can be both harmful and helpful

Characteristics of EM waves Light is only a teeny part of all EM waves The electromagnetic spectrum is the entire range of EM waves Divided by wavelength and frequency

Radio Waves Longest wavelengths (30+ cm) Lowest frequencies Used for broadcasting radio signals Modify frequency or amplitude (height) of wave AM and FM radio

Radio Waves FM versus AM Radio AM has longer wavelengths AM bounce off atmosphere FM less affected by electrical “noise” Why FM sounds better

Radio waves and Television TV signals carried by radio waves Shorter wavelengths than radio Higher frequencies than radio Change frequency and amplitude Sent to satellites to amplify signal

Microwaves Shorter wavelengths (1mm-30cm) and higher frequencies than radio Microwave ovens, Radar and communication

Radar From microwaves Radio detection and ranging Finds speed and location of object Sends waves that bounce off items

Infrared Waves Shorter wavelengths (700 nm to 1mm) and higher frequencies than microwaves “Warm” feeling on sunny day Heat Invisible for us, but can be detected--thermogram

Visible Spectrum Narrow range of wavelengths and frequencies that humans can see White light is the combination of all colors of light

Ultraviolet Light Shorter wavelengths (60-400nm) and higher frequencies than visible light Both good and bad for your body

Ultraviolet Light Good Effects Bad Effects Kill bacteria on food Sterilize surgical tools Helps body make vitamin D Helps with calcium absorption Bad Effects Sunburn Skin cancer, wrinkles, eye damage Protected by ozone, clothing and sunscreen

X rays and Gamma Rays X rays Gamma rays .001nm-60nm wavelength Medical field Kill cells Lead aprons Airport security Gamma rays Shortest wavelengths (<0.1nm) and highest frequency Penetrate almost all materials Treat cancer Kill cells Kill bacteria on food

Section 2—The electromagnetic Spectrum Objectives Identify the two ways that EM waves differ from each other Describe some uses for radio waves and microwaves List examples of how infrared waves and visible light are important in your life Explain how ultraviolet light, X rays, and gamma rays can be both harmful and helpful

Section 3—Interactions of Light Waves Objectives Describe how reflection allows you to see things Describe absorption and scattering Explain how refraction can create optical illusions Explain how refraction can separate white light into colors Compare constructive and destructive interference of light

Reflection Reflection is when light waves bounce off an object EX: mirror The Law of Reflection states that the angle of incidence is equal to the angle of reflection The angle it comes in is the same angle it goes out

Types of Reflection Regular Reflection is when all light beams are reflected at the same angle Smooth surfaces Diffuse Reflection is when light beams reflect at many different angles Not smooth

Light Source or Reflection? Luminous objects produce visible light Light source Illuminated objects are visible objects that are not a light source Due to the light around it (reflection

Absorption and Scattering Absorption is the transfer of energy carried by light waves to particles of matter Air absorbs some energy Why a flashlight dims Farther the light source, the more light that gets absorbed

Absorption and Scattering Scattering is an interaction of light with matter that causes light to change direction All directions See objects outside beam WHY THE SKY IS BLUE!

Refraction Refraction is the bending of a wave as it passes at an angle from one substance to another

Refraction Why does refraction happen Light travels at different speeds when it goes through different things

Refraction When light switches materials, it speeds up or slows down This changes the angle

Diffraction Diffraction is the bending of waves around barriers or through openings Depends on wave size Depends on barrier size

Diffraction and Wavelength Small wavelength for light! Does not bend much unless opening is even smaller Why light does not bend around corners

Interference Interference is a wave interaction that happens when two or waves overlap Can brighten: constructive Can dim: destructive

Constructive v. destructive interference

Section 3—Interactions of Light Waves Objectives Describe how reflection allows you to see things Describe absorption and scattering Explain how refraction can create optical illusions Explain how refraction can separate white light into colors Compare constructive and destructive interference of light

Section 4—Light and Color Objectives Name and describe the three ways light interacts with matter Explain how the color of an object is determined Describe color addition and color subtraction

Light and Matter When light strikes objects, it can be Reflected Absorbed Transmitted

Reflection, Absorption,Transmission Reflection is when light bounces off an object Absorption is when light energy is transferred to matter Transmission is the passing of light through matter

Types of Matter Transparent matter is matter through which visible light is easily transmitted Ex: glass, plastic wrap

Types of Matter Translucent matter transmits light but also scatters it Ex: frosted glass, wax paper

Types of Matter Opaque matter is matter that does not transmit any light Ex: Aluminum foil, a book, wood

Colors of Objects Color is about the reflection of light off materials that hits your eyes

Colors of objects Translucent objects Opaque objects The colors you see are the colors that are transmitted Opaque objects The colors you see are the colors that are reflected White = ALL colors reflected Black = ALL colors absorbed

Mixing colors of light Only need 3 colors to make white light Red Green Blue Called primary colors of light

Color addition Combining colors of light is called color addition Mixing two primary light colors makes secondary light colors

Colored Television Television has color because each “dot” has a group of red, green, and blue dots Different combinations give us color

Mixing colors of pigment A pigment is a material that gives a substance its color by absorbing some color of light and reflecting others Primary pigments Magenta Yellow Cyan

Color subtraction Mixing pigments results in more colors being absorbed or taken away—color subtraction

Section 4—Light and Color Objectives Name and describe the three ways light interacts with matter Explain how the color of an object is determined Describe color addition and color subtraction