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The Nature of Light

The Nature of Light. Let’s Review…. What are some of the differences between sound waves and light waves?. Sound Waves Mechanical wave Longitudinal wave Requires a medium to travel through Created by vibrations Speed of Sound: 343 m/s. Light Waves Electromagnetic wave

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The Nature of Light

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  1. The Nature of Light

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

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

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

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

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

  7. Why does a flashlight appear brighter when you are near it? • 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.

  8. In addition to being reflected and absorbed….light can bend • 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.

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

  10. Summary • 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?

  11. 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. • Hint: remember the formula for speed

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

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

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

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

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

  17. Opaque • 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…

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

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

  20. Electromagnetic Spectrum • 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.

  21. Radio Waves • 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)

  22. Microwaves • Used for communication, weather radar and cooking food

  23. Infrared • Waves in the form of heat…

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

  25. Wavelength and Frequency of Visible Light Indigo has a wavelength of 445nm and 673 THz Indigo has a wavelength of 445nm and 673 THz A THZ is a terahertz which is 10 12 Hertz

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

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

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

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