Part 1 – Properties of Light

1. Laser Part 1 – Properties of Light • Light travels in straight lines:

2. Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

3. Thunder and lightning start at the same time, but we will see the lightning first. • 2) When a starting pistol is fired we see the smoke first and then hear the bang.

4. We see things because they reflect light into our eyes: Homework

5. A luminous object is one that produces light. A non-luminous object is one that reflects light. • Luminous and non-luminous objects Luminous objects Reflectors

6. Rays of light Shadows are places where light is “blocked”: • Shadows

7. Part 2 - Reflection • Reflection from a mirror: Normal Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

8. The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it hits it. The same !!!

9. Clear vs. Diffuse Reflection • Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

10. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet

11. Adding colours • White light can be split up to make separate colours. These colours can be added together again. • The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

12. Homework Seeing colour • The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

13. A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

14. Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider a football kit: Shirt looks red White light Shorts look blue

15. In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Shirt looks black Blue light Shorts look blue

16. What can a light wave do when it encounters matter? • Be TRANSMITTED • laser aimed at water or glass • Be REFLECTED • specular reflection of light by a mirror • diffuse reflection of the light in this room off all the other students • reflection is re-radiation of light by the electrons in the reflecting material • Be ABSORBED • Cyan light shining on a red apple is absorbed by electrons in the apple • Something new!! • A light wave shining on molecules in the air or plastic or other “transparent” materials can be: • SCATTERED • Light ray moves over to the side in all directions rather than forward, backward or being absorbed. • Intensity of the scattered light can depend on wavelength

17. Amplitude(maximum height) The intensity of the light is proportional to the amplitude squared. Large amplitude means bright light. Low amplitude means dim light Ray Waveform Wavelength Speed of light in empty space is c = 3 x 108 meters/sec

18. Light consists of electric (and magnetic) fields moving through space at the speed of light

20. The Electromagnetic Spectrum • Human eyes are only able to process information from the visible part of the spectrum • Toward longer wavelengths, the spectrum includes infrared light, microwaves, and radio • Toward shorter wavelengths, the spectrum includes ultraviolet light, X-rays, and gamma rays • All of these are forms of electromagnetic radiation

21. Wavelengths of Light - Visible • What we see as white light is actually made up of a continuum of components • Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV) • There is actually a continuous transition of color, each with its own wavelength and frequency

22. Wavelengths of Light - Visible • Red light has an approximate wavelength of 7.0 x 10-7 m and a frequency of 4.3 x 1014 Hz • Violet light has an approximate wavelength of 4.0 x 10-7 m and a frequency of 7.5 x 1014 Hz

23. Scattering

24. Types of Scattering in the Atmosphere • Rayleigh • Mie • Geometric

25. Rayleigh Scattering in Visible Spectrum • Blue sky • Red Sunset • Blue water (from underwater)

26. Think of white light from sun as a mixture of R, G and B Blue is scattered the most so sky looks blue when we look away from the sun What is Rayleigh scattering?(or why is the sky blue) • The shorter the wavelength, the more light is scattered • blue is scattered more than red. • this is why the sky is blue and sunsets are red.

28. Color of Day-time sun vs. Sunset Rays from Sun (not scattered) Earth Atmosphere White or yellow

29. Red Sun/sky during the Sunset

30. Light scattering in milk and smoke? • Larger particles scatter red as well as blue and hence look white. • Dust or smoke • Clouds; • Milk; • There are many • other types of • scattering…

31. Mie Scattering • Explains scattering around larger droplets such as Corona around the sun or moon, and similar phenomena.