Physics 1230: Light and Color

Size: px

Start display at page:

Download "Physics 1230: Light and Color"

Richard Burke
5 years ago
Views:

1 Physics 1230: Light and Color Chuck Rogers, Ryan Henley, Valyria McFarland, Peter Siegfried physicscourses.colorado.edu/phys1230 Congratulations on completing Exam 1. Great job! Exam 1 Average: 76 +/- 12 of 100 points Group Exam Average: 86 +/- 10 of 100 points. Come down and collect your Exam 1. Get a diffraction grating if needed. 1

2 Physics 1230: Light and Color Chuck Rogers, Ryan Henley, Valyria McFarland, Peter Siegfried physicscourses.colorado.edu/phys1230 Exam 1 Questions?? 1. Write your question on a separate page. 2. Attach to otherwise untouched exam. 3. Bring it to Prof. Rogers and I will have a look. 4. Try to ask questions by Thurs. next week. 2

3 Physics 1230: Light and Color Chuck Rogers, Ryan Henley, Valyria McFarland, Peter Siegfried physicscourses.colorado.edu/phys1230 Lecture 11: Atoms and light: Luminescence. Start discussing about Reflection and Images 3

4 Last Time: There are two main ways to 1. Incandescence: Heat an object up, and it glows. ( Blackbody radiation ) make light 2. Luminescence: For example discharge lamp

Electrons jiggle in hot things emit light PhET radio waves

5 Last Time: Incandescence Hot things glow = incandescence Current runs through the filament This makes the filament hot Electrons jiggle in hot things emit light PhET radio waves Heating objects causes their electrons to jiggle and they emit light.

6 Last Time: Wien s Law: Brightest color wavelength multiplied by the absolute temperature is a constant. T brightest meters Kelvin Tell me the brightest color of a hot object and I can tell you how hot it is!

7 Wien s Law tells about brightest wavelength. But other waves are created too. Hot objects radiate at all wavelengths.

levels) The more energy the electron has, the further away it is from

8 Last Time: Key points about atoms Electrons are bound to atoms There are only certain amounts of energy the electrons can have (energy levels) The more energy the electron has, the further away it is from nucleus (higher energy level) These are both simplified models of atom 8

9 Atoms can absorb energy (e.g., light) Then, the electron moves up an energy level + We say a PHOTON is absorbed. Photon energy is proportional to frequency of the light. E = hf 9

10 Atoms can emit energy (e.g. light) One color (f) only We say a PHOTON is emitted Spacing between energy levels leads to the color emitted: E = hf

11 Gas discharges!

12 Which type of light has the highest energy per photon? A. Red light B. Blue light C. X-ray light D. Radio E = hf

13 High frequency light photons have higher energy E = hf Low E High E

14 High frequency light has higher energy This is why we limit our exposure to UV and X-rays

15 The latest in lighting: LED

16 Another example of luminescence: Lasers: Light Amplification by Stimulated Emission You don t have to know how they work. But very important part of modern technology. In the category of luminescence.

17 Breathe in Breathe out. Where are we in the course? Unit 1: What is light? Unit 2: Light as a wave finishing polarization Unit 3: Light sources and spectra Unit 4: Reflection Unit 5: Refraction Unit 6: Lenses Unit 7: Eye and camera Unit 8: Color perception Unit 9: Visual perception, illusion, art Unit 10: TBD

18 Recall: Light as a ray Light travels in straight lines from a source It travels in all directions from each spot on an extended source We can predict all sorts of useful phenomena by drawing light ray diagrams : Pinhole camera, Shadows in sun What if light interacts with a material reflects off, transmits through how do we extend ray ideas?

19 What can happen to incoming light Silver, water Black pavement Important parameters: Frequency of light Nature of material Glass Or any partial combination of these things

20 Flashlight shining at mirror Basic reflection: Light on mirror

21 Equal angle rule q i = angle of incidence q r = angle of reflection q i = q r is specular reflection Incident Ray q i q r Reflected Ray Normal Mirror A normal is a line perpendicular to the surface. 21

22 Light on mirror versus white card Flashlight shining at mirror Flashlight shining at white paper card Does light still obey the law of reflection in the case of the white paper card??

23 Specular or diffuse? Diffuse reflection (paper) Specular reflection (mirror) Diffuse transmission (wax paper) 23

24 Law of reflection? Reflection can be Specular (mirror-like) But most things reflect diffusely Still follows law of reflection at each little interface

25 Law of reflection? Which best describes the images: A) smooth water is specular and wavy water is diffuse B) wavy water is specular and smooth water is diffuse

26 Activities: How do we use law of reflection to understand mirrors? Get together with a few group members, Delegates get activity sheets (one per member), mirror, etc.

27 Activities: How do we use law of reflection to understand mirrors? Part 1: Where is the image? Click A when you have finished page 1.

28 Images There are some light rays. Some reach the eye. The eye/brain interprets these rays as? A) A white wall B) A single white line C) A point of light D) Something else

29 Good place to stop!

Lecture 5 Chapter 1 & 2. Sources of light

Lecture 5 Chapter 1 & 2. Sources of light We are here Lecture 5 Chapter 1 & 2 Some history of technology How vision works What is light Wavelength and Frequency: c = f λ Scientific notation and metric units Electromagnetic spectrum Transmission