PHYSICS - Chapter 16. Light and Color and More

Transcription

1 PHYSICS - Chapter 16 Light and Color and More

2 LIGHT-fundamentals 16.1 Light is the visible part of the electromagnetic spectrum. The electromagnetic spectrum runs from long Radio and TV waves to short x-rays and gamma-rays. Light is defined as the electromagnetic rays that stimulate the retina of the human eye.

3 LIGHT-fundamentals 16.1 AM waves TV Waves and FM Waves Microwaves Infrared Visible Light Ultraviolet X-Rays Gamma Rays TYPES OF ELECTROMAGNETIC WAVES

4 LIGHT-fundamentals 16.1

5 LIGHT-fundamentals 16.1

6 LIGHT-fundamentals 16.1 Electromagnetic waves have frequency and wavelength Frequency=the number of oscillations measured in hertz Wavelength=The shortest distance between points where a wave pattern repeats itself (meters)

7 LIGHT-fundamentals 16.1 WAVELENGTH

8 LIGHT-fundamentals 16.1 Electromagnetic Waves are measured by their wavelength Radio waves = 1 x 10 4 meters Gamma waves = 1 x meters

9 LIGHT-fundamentals 16.1 Light Wavelengths Red= 7 x10 7 m Violet = 4 x 10 7 m

10 LIGHT-fundamentals 16.1 Roy G. Biv RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET

11 LIGHT-fundamentals 16.1 Light travels in a straight line in a vacuum. Ray Model of light describes how light travels in a straight line. Good for optics but ignores the wave nature of light.

12 LIGHT-fundamentals 16.1 Speed of Light-originally thought to be instantaneous Roemer (Danish) measured speed of light from Io (moon of Jupiter) Compared time when Io emerged from Jupiter s orbit 14 sec. Difference when Earth was moving toward Jupiter then when moving away

13 LIGHT-fundamentals 16.1 Ole Roemer

14 LIGHT-fundamentals 16.1

15 LIGHT-fundamentals 16.1 Roemer found that speed of light could be measured. Measurements slightly off by today s standard. Michelson measured time it took light to travel between two mountains in CA x 10 8 m/s Today we use 3.00 x 10 8 m/s as speed of light

16 LIGHT-fundamentals 16.1 Speed of light is is a universal value and is represented by c. Speed is equal to the product of frequency and wavelength λ = lambda = wavelength C = λf

17 LIGHT-fundamentals 16.1 What is the frequency of yellow light, λ = 556 nanometers? C = λ f f = c / λ F =3.00 x 10 8 m/s / 556 x 10 9 m = x10 17 Hz = 5.40 x Hz

18 LIGHT-fundamentals 16.1 Complete Problems 2, 3, 4 and 5 page 376 Note: there are 3.28 ft/m (number 2) Note: 1 femtosecond = seconds (3a) Answers on page 799

19 LIGHT-fundamentals 16.1 Sources of Light Luminous Body emits light waves (sun) Illuminated Body reflects light waves (moon) Luminous Flux is rate at which a luminous body emits light (P)

20 LIGHT-fundamentals 16.1 Typical 100-watt light bulb emits 1750 lm Illuminance (E) = rate at which light falls on a surface Measured in lumens / meter 2 or lux (lx)

21 LIGHT-fundamentals 16.1 Inverse Square Law = If the distance a surface is moved from a point of light is doubled, the illuminance is reduced by a factor of four. This is an inverse square relationship This is why a flash in photography effectiveness falls off rapidly.

22 LIGHT-fundamentals 16.1

23 LIGHT-fundamentals 16.1 Candela (cd) is a measure of the intensity of light. Describes the amount of light that falls on a 1 m 2 of a sphere 1 m in diameter. For a brighter light, you must get closer or use a brighter bulb. (well, duh!)

24 LIGHT-fundamentals 16.1 Illuminance E (lux = lx) E = P / 4π d 2 P = luminous flux (lumen - lm)

25 LIGHT-fundamentals 16.1 Q: What is the illumination on your desktop if it is lighted by a 1750-lm lamp that is 2.5 m above your desk? A: E = P / 4π d 2 = 1750 lm / 4 π (2.5 m) 2 = 22.3 lm/m 2 = 22.3 lx

26 LIGHT-fundamentals 16.1 Complete problems 6, 7, 9 page 381 Answers on page 799 Turn in seven problems(35 pts)

27 LIGHT-fundamentals 16.2 Transparent-Transmit light waves w/o distortion Translucent-Transmit light waves w/ distortion Opaque-Does not transmit light

28 LIGHT-fundamentals 16.2 Color Spectrum-ordered arrangement of colors from violet to red (Newton)

29 LIGHT-fundamentals 16.2 Color by addition-making white light by adding the correct amounts of red, green, and blue light (color TV tube) Red, Green, and Blue are the PRIMARY Colors of light

30 LIGHT-fundamentals 16.2

31 LIGHT-fundamentals 16.2 Red + Green = Yellow Blue + Green = Cyan Red + Blue = Magenta Yellow, Cyan, and Magenta are the secondary colors

32 LIGHT-fundamentals 16.2

33 LIGHT-fundamentals 16.2 Yellow + Blue = White So, Yellow is Complimentary to Blue Cyan and Red are Complimentary Magenta and Green are Complimentary

34 LIGHT-fundamentals 16.2 Dyes=absorb certain wavelengths and reflects others. If white light hits a tomato blue and green are absorbed and red is reflected. Pigments are similar to dyes but are larger molecules.

35 LIGHT-fundamentals 16.2

36 LIGHT-fundamentals 16.2 Soap Bubbles and oil slicks are thin film. Think of spectrum-like colors Formed by constructive and destructive interference of light waves = thin-film interference

37 LIGHT-fundamentals 16.2 SOAP BUBBLE

38 LIGHT-fundamentals 16.2 OIL FILM

39 LIGHT-fundamentals 16.2 Polarized light-only allows waves that are vibrating in the same plane to pass through.

40 LIGHT-fundamentals 16.2

41 Light-Chapter 17 REFLECTION AND REFRACTION Southern Boone County HS Bill Palmer

42 Light-Chapter 17 Rainbows Look at the following pictures of rainbows and see what conclusions you can form.

43 Light-Chapter 17 Rainbows

44 Light-Chapter 17 Rainbows

45 Light-Chapter 17 Rainbows

46 Light-Chapter 17 Did you catch the following: The sun must be shining for a rainbow. There must be rain for a rainbow. The sky is brighter inside the rainbow. In the secondary rainbow, the order of the colors are reversed. These occur because the light is reflected and refracted to form the rainbow.

47 Light-Chapter 17 REFLECTION-Angle of incidence is equal to the angle of reflection. A regular reflection comes from a smooth mirror-like surface. A diffuse reflection comes from a rough surface like paper. The irregularities in the paper are giant compared to the wavelength of lignt.

48 Light-Chapter 17

49 Light-Chapter 17 Refraction-When a beam of light passes from one object to an object of a different density. If light goes from air to glass at an angle it is bent.

50 Light-Chapter 17

51 Light-Chapter 17 Snell s Law: The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. N = sine I / sine r

52 Light-Chapter 17 Indices of Refraction of various materials have been calculated in the lab. Vacuum = 1.00 Air = Water = 1.33 Ethanol = 1.36 Crown Glass = 1.52 Quartz = 1.54 Flint Glass = 1.61 Chart on page 397

53 Light-Chapter 17 A light beam in air hits a sheet of crown glass at an angle of At what angle is it reflected? Known: n i = 1.00 ( rounded to sig fig) n r = 1.52

54 Light-Chapter 17 n i (sin i = n r (sin r sin r = n i / n r (sin i sin r = (1.00/1.52) (.500) sin r =.329 sin r =

55 Light-Chapter 17 Problems: 1-4, page 400. Work Provided Problems 5-8, page 402, Work Provided Problems 31-43, page Answers Provided.