1. Chapter 26 Light Herriman High Physics

2. The Definition of Light The current scientific definition of Light is a photon carried on a wave front. This definition incorporates the dual nature of light, which means that light behaves both like a particle and a wave. Light is a form of electromagnetic radiation – that means that it does not require a medium to travel through. All electromagnetic radiation travels at 3 x 10 8 m/s Herriman High Physics

3. Electromagnetic Waves The electromagnetic spectrum is a range of waves extending from radio waves to gamma waves. The lowest frequency of light that we can see is red in color – all waves below that are called infrared. The highest frequency of light that we can see is violet in color and any frequencies that are higher than that are said to be ultraviolet. Herriman High Physics

4. Transparent and Opaque Materials that transmit all of the light which they receive are said to be transparent. They let light through. Materials which absorb light without reemission are said to be opaque – they do not let light through. Herriman High Physics

5. Shadows A shadow is caused when an object block light from a source. A shadow has two parts: Umbra – total shadow – no light received. Penumbra – partial shadow – some light received, some blocked. Herriman High Physics

6. Chapter 27 Color Herriman High Physics

7. The Colors of Light Light is defined as the frequencies of electromagnetic radiation which stimulate the human retina. Light ranges in color from: Red - lowest frequency/longest wavelength Orange Yellow Green Blue Indigo Violet – highest frequency/shortest wavelength Herriman High Physics

8. White Light and the Color Black White light contains all of the colors (frequencies) of visible light. Black is the absence of light. Vision is the process of seeing reflected light. The color that you see is reflected from an objects – all other wavelengths are absorbed. Herriman High Physics

9. Color by Transmission The color of a transparent object depends upon the color it transmits. The material which selectively absorbs colors of light is called a pigment. Absorbed light warms the object – hence darker colors tend to get warm in sunlight and lighter colors tend to remain cooler. Herriman High Physics

10. Mixing Light When red, blue and green light (primary colors) are mixed, new colors are formed (secondary colors). All three colors form white light. Red and Green – yellow Red and Blue – magenta Green and Blue - Cyan Herriman High Physics

11. Mixing Pigments When you mix pigments (paints) you add by subtraction – that is each pigment you add to your mixture subtracts a color of light. Primary pigments Magenta Yellow Cyan Secondary Mixtures Yellow and Cyan – Green Yellow and Magenta – Red Magenta and Cyan - Blue Herriman High Physics

12. Chapter 28 Reflection and Refraction Herriman High Physics

13. Reflection When a wave reaches a boundary between two media and is turned back – this is reflection Total reflection –boundary with a more rigid medium Partial reflection – less rigid medium. Herriman High Physics

14. Law of Reflection The law of reflection states that the angle of incidence = angle of reflection Incident ray Reflected ray Angle of incidence Angle of reflection Herriman High Physics

15. Mirrors Plane mirrors are flat mirrors which form a virtual image. A virtual image is one which forms on the opposite side of the mirror. Images are the same size as the object and the same vertical orientation. Herriman High Physics

16. Curved Mirrors: Concave and Convex Concave Mirror Curves inward Close objects Form a virtual image which is larger than the object Objects further away form real images which are cast on a screen Convex Mirror Curves outward Close objects form a virtual image which is smaller than the object These mirrors are used to give a wide field of view Herriman High Physics

17. Refraction Refraction is the bending of light at a boundary. If the speed in the new media is less than the speed in the old, the wave bends toward the normal If the speed in the new media is more than the speed in the old, the wave bends away from the normal. Sidewalk Grass Herriman High Physics

18. Snell’s Law and the Index of Refraction How much light bends at a boundary is given by Snell’s Law or the Index of refraction: Another way that this law is written is: n 0 sin i = n sin r Where n 0 is the index for the material you are moving out of and n is the index for the material you are going into. Herriman High Physics

19. Sample Problem What is the speed of light in crown glass if its index of refraction is 1.52? What is the angle of refraction for a wave in crown glass if its angle of incidence is 30°. Assume that it is coming from air into a cube of the glass. Herriman High Physics

20. Solution n 0 sin i = n sin r 1 sin 30° = 1.52 sin r 1 sin 30°/1.52 = sin r r = 19.73° Herriman High Physics

21. Dispersion through a Prism Dispersion through a prism is a form of refraction. Atmospheric refraction is what causes a rainbow. Herriman High Physics

22. Converging and Diverging Lenses Converging lenses are convex, or curve outward. Diverging lenses are concave, or curve inward. Herriman High Physics

23. The Eye The lens of a human eye focuses an image on the retina at the rear of the eye. If the lens forms an image in front of the retina, then a person is said to be nearsighted If the lens form an image at the rear of the retina (behind it) then the person is said to be farsighted. Herriman High Physics

24. Corrective Lenses Since a nearsighted person’s eye forms the image too soon, the lens of their eye has too much convergence, hence a diverging lens, (concave) is used to separate the rays of light coming from the object so that the image will converge on the retina. Since a Farsighted person’s eye forms the image after the retina, a converging lens, (convex) is used to help the rays of light converge sooner, forming the image on the retina. Herriman High Physics