The Nature of Light

Let’s Review… What are some of the differences between sound waves and light waves? What are some of the differences between sound waves and light waves?

Sound Waves Mechanical wave Mechanical wave Longitudinal wave Longitudinal wave Requires a medium to travel through Requires a medium to travel through Created by vibrations Created by vibrations Speed of Sound: Speed of Sound: 343 m/s 343 m/s Light Waves Electromagnetic wave Electromagnetic wave Transverse wave Transverse wave DOES NOT require a medium to travel through DOES NOT require a medium to travel through Created by vibration of electrically charged particles Created by vibration of electrically charged particles Speed of Light: Speed of Light: 300,000,000 m/s

Bellringer Why can you see your reflection in a mirror and not off of a brick wall? Why can you see your reflection in a mirror and not off of a brick wall?

Interactions of Light Waves What is reflection? What is reflection? Why does light bounce differently off of different objects? Why does light bounce differently off of different objects? How can you change the way a ball will go when you bounce it? How can you change the way a ball will go when you bounce it?

Law of Reflection The Law of Reflection states that the angle of incidence is equal to the angle of reflection. The Law of Reflection states that the angle of incidence is equal to the angle of reflection. Light Source

Why does a flashlight appear brighter when you are near it? Absorption…….what does this word mean to you Absorption…….what does this word mean to you Just like a sponge soaking up water, particles of matter can absorb the energy from waves of light. When there is enough matter (including air) to absorb it, there is none left for us to see. Just like a sponge soaking up water, particles of matter can absorb the energy from waves of light. When there is enough matter (including air) to absorb it, there is none left for us to see.

In addition to being reflected and absorbed….light can bend Refraction and diffraction are two different types of bending….. Refraction and diffraction are two different types of bending….. Even though it is bending, the light is passing THROUGH an object…this is called transmission. Even though it is bending, the light is passing THROUGH an object…this is called transmission.

Refraction Light bends when it travels from one medium to another (changes speed) Light bends when it travels from one medium to another (changes speed)Diffraction Light bending to go around a corner or through an opening. Light bending to go around a corner or through an opening.

Summary What are the 3 main things that light waves do when they interact with matter? What are the 3 main things that light waves do when they interact with matter? Which of these occurs as light makes it way from the sun to your eyes? Which of these occurs as light makes it way from the sun to your eyes?

Bellringer Calculate the time it takes for light from the sun to reach Mercury. Mercury is 54,900,000,000 meters away from the sun. Calculate the time it takes for light from the sun to reach Mercury. Mercury is 54,900,000,000 meters away from the sun. Hint: remember the formula for speed Hint: remember the formula for speed

Bellringer speed = distance/time time = distance/speed time = 54,900,000,000 m = 183 seconds 300,000,000 m/s 300,000,000 m/s

Just to review… What are 3 things that can happen to light when it strikes an object? What are 3 things that can happen to light when it strikes an object? 1. Reflect 2. Absorb 3. Transmit (bend, but go through)

The combination of reflecting, absorbing and transmission determines what you see when you look at an object

Transparent An object is transparent (or see through) when light is easily able to pass through it. An object is transparent (or see through) when light is easily able to pass through it.

Translucent When some light is scattered as it tries to pass through an object, it causes a blurry appearance…this is translucent…. When some light is scattered as it tries to pass through an object, it causes a blurry appearance…this is translucent….

Opaque If an object absorbs some colors and reflects the rest, we say it is opaque….which means you can’t see through it If an object absorbs some colors and reflects the rest, we say it is opaque….which means you can’t see through it The color reflected back would be the color that we see….all others would be abosorbed… The color reflected back would be the color that we see….all others would be abosorbed…

Bellringer What are 3 ways that light can interact with other objects? What are 3 ways that light can interact with other objects? What are 3 ways that those interactions can cause objects to appear? What are 3 ways that those interactions can cause objects to appear?

Vocabulary Quiz Light Light White Light White Light Transparent Transparent Translucent Translucent Opaque Opaque Lens Lens Mirror Mirror Prism Prism Electromagnetic Wave Electromagnetic Wave Electromagnetic Spectrum Electromagnetic Spectrum

Electromagnetic Spectrum EM energy is created by vibrations that carry energy….each EM wave emits a different energy level. EM energy is created by vibrations that carry energy….each EM wave emits a different energy level. All of these waves together are known as the electromagnetic spectrum. All of these waves together are known as the electromagnetic spectrum.

Radio Waves Lowest energy of light – longest wavelength – used for communication since they travel long distances… Lowest energy of light – longest wavelength – used for communication since they travel long distances… (Radio waves are NOT sound waves…they only become sound when they are received by a radio and changed into sound) (Radio waves are NOT sound waves…they only become sound when they are received by a radio and changed into sound)

Microwaves Used for communication, weather radar and cooking food Used for communication, weather radar and cooking food

Infrared Waves in the form of heat… Waves in the form of heat…

Visible Light Range of wavelengths that the human eye can detect…. Range of wavelengths that the human eye can detect…. Red has longest wavelength Violet has the shortest wavelength

Wavelength and Frequency of Visible Light Indigo has a wavelength of 445nm and 673 THz A THZ is a terahertz which is Hertz

Ultraviolet Light Wavelengths that are just “beyond violet” on the spectrum Wavelengths that are just “beyond violet” on the spectrum Carry more energy than visible light Carry more energy than visible light Will cause skin damage Will cause skin damage

X-Rays Used for imaging – can travel well through soft substances….not as well through dense materials Used for imaging – can travel well through soft substances….not as well through dense materials

Gamma Rays Gamma Rays – highest energy light – shortest wavelength - damaging to cells – used to sterilize medical equipment – Gamma Rays – highest energy light – shortest wavelength - damaging to cells – used to sterilize medical equipment – Used to treat cancer Used to treat cancer