LIGHT. Speed of light Law of Reflection Refraction Snell s Law Mirrors Lenses

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1 LIGHT Speed of light Law of Reflection Refraction Snell s Law Mirrors Lenses

2 Light = Electromagnetic Wave Requires No Medium to Travel Oscillating Electric and Magnetic Field Travel at the speed of light v max = c = m/s Energy Determined by Frequency

3 Visible Light Small Portion of Electromagnetic Spectrum 400nm 750 nm

4 Calculating the Speed of Light The Michelson Experiment: Measured the speed of light (1920 s)

5 Light Behavior: REFLECTION Law of Reflection: Angle of Incidence =Angle of Reflection Angle measure with respect to a Normal Line

6 REFLECTION Two Types of Reflection Diffuse Reflection: Parallel rays are scattered after reflection (Image cannot be seen) Specular Reflection: Parallel rays are reflected parallel to each other (image can be seen)

7 Ray Diagram for a Plane Mirror object Image (virtual) Two rays from a single point on an object. 1) parallel to axis, reflects parallel to axis 2) towards center of mirror, reflects at equal angle 3) trace reflected rays behind mirror 4) Intersection is location of virtual image

8 Refraction: Bending of a wave as it enters new medium Velocity decreases Light changes speed as it enters a new medium. Change in speed causes a change in direction Ratio of speed in a vacuum to speed in the material is the index of refraction Velocity increases n = C V

9 Refraction: Examples

10 Rainbows: Refraction, Reflection Interference

11 Snell s Law: The angle of refraction depends on the two indices of refraction n 1 sinθ 1 = n 2 sinθ 2 Example 1: n 1 = air, ϴ 1 = 25 o n 2 = water, ϴ 2 =? o Example 2: n 1 = Diamond, ϴ 1 = 20 o n 2 =?, ϴ 2 = 30 o

12 Snell s Law: Total Internal Reflection Occurs when the refracted angle is greater than or equal to 90 o Light reflects back into material Critical Angle = angle of incidence for which the angle of refraction is 90 o. n 2 >n 1

13 Lenses: Convex Lens Converging Lens Focal Length = point where parallel rays intersect positive focal length= distance from center of lens to focal point Produces both real and Virtual images

14 Convex Lens: Real Image Object Distance Greater than focal length Image distance greater than focal length Positive image distance Image is inverted (negative height) 1 d d i = 1 f Magnification m = h i h 0 = d i d o

15 Example: Real Image A candle 5cm tall is placed 15 cm from a convex lens with a focal length of 10 cm. Where is the image? How Tall is the image? Draw ray diagram.

16 Convex Lens: Virtual Image Object Distance Less than focal length Image distance is negative Image is Upright (positive height) 1 d d i = 1 f Magnification m = h 1 h 0 = d i d o

17 Example: Virtual Image An candle 2cm tall is placed 5 cm from a convex lens with a focal length of 10 cm. Where is the image? How Tall is the image? Draw ray diagram.

18 Concave Lens: Virtual Images only Diverging Lens Focal Length is Negative Image distance is Negative Image is Upright (positive height) Image is Smaller 1 d d i = 1 f

19 Example: Concave Lens An candle 6cm tall is placed 5 cm from a concave lens. The image is 2 cm tall. Where is the image? What is the focal length?

20 Mirrors: Concave and Convex Shaped like sections of a sphere, reflective on the inside (concave) reflective on the outside (convex).

21 Curved Mirrors: Concave Mirror Focal length = ½ *radius Produces both real and virtual Images Produces both larger and smaller images Convex Mirror Negative Focal length = ½ *radius Produces virtual Images Produces smaller images

22 Concave Mirror Behave like convex Lens REAL IMAGE Object Distance Greater than focal length Image distance greater than focal length Positive image distance Image is inverted (negative height) 1 d d i = 1 f Magnification m = h 1 h 0 = d i d o

23 Example: Virtual Image A candle 4cm tall is placed 12 cm from a concave mirror with a radius length of 8 cm. What is the focal length? Where is the image? How Tall is the image? Draw ray diagram.

24 Concave Mirror: Virtual Image Object Distance Less than focal length Image distance is negative Image is Upright (positive height) 1 d d i = 1 f Magnification m = h 1 h 0 = d i d o

25 Convex Mirror Behave like Concave Lens Focal Length is Negative Image distance is Negative Image is Upright (positive height) Image is Smaller