Upcoming SlideShare
×

Photometry and interactions

713 views

Published on

0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

Views
Total views
713
On SlideShare
0
From Embeds
0
Number of Embeds
13
Actions
Shares
0
26
0
Likes
0
Embeds 0
No embeds

No notes for slide

Photometry and interactions

1. 1. LIGHT: MEASURABLE PROPERTIES AND INTERACTIONS Understanding Light Phenomena
2. 2. Contents Calculating speed of light  Photometry  Interactions of Light and Matter 
3. 3. CALCULATING SPEED OF LIGHT
4. 4. Speed of Light Fastest recorded speed of object in the universe  Approximately equal to 3 x 108 m/s or 186,000 mi/s 
5. 5. Ole Roemer Danish astronomer who made the first successful estimation of the speed of light (1675)  Involved astronomical observations of one of satellites of Jupiter  Speed of light was estimated to be 2.3 x 108 m/s 
6. 6. Roemer’s Observation
7. 7. Fizeau’s Method The first successful method for measuring the speed of light by means of purely terrestrial techniques (1849)  Performed by French physicist Armand H. L. Fizeau  Arrived at a value of 3.1 x 108 m/s 
8. 8. Fizeau’s Setup
9. 9. c = 2.9979 x 8 10 m/s
10. 10. PHOTOMETRY
11. 11. Photometry The measurement of brightness of a light source  There are three measurable quantities of light  ◦ Luminous intensity (I) ◦ Luminous flux (F) ◦ Illumination (E)
12. 12. Luminous Intensity The brightness of a light source  Measured in terms of candela  Candela is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian 
13. 13. Luminous flux A measure of the radiant power of light emitted from a source without regard for the direction in which it is emitted  Measured in terms of lumens (lm)  F = 4ΠI 
14. 14. Illuminance The amount of illumination  The amount of luminous flux falling on a unit area of surface  Measured in terms of lumens per square meter or lux  E = F/A 
15. 15. Sample Problem  A light source of 500 cd is placed 4 m above the floor of a big hall. ◦ Find the total luminous flux emitted by the source. ◦ Find the intensity of illumination on a point directly below the source.
16. 16. Recommended Intensities of Illumination Place Illuminance (lux) Library 200-250 Basketball court 200-250 Classroom or 300-400 office Drafting or sewing 500-800 room
17. 17. Typical Luminous Efficiency Source Tungsten filament 20 W 40 W 60 W 100 W Fluorescent lamp 20 W 40 W Sodium vapor lamp Efficiency 10 12 14 16 50 75 55
18. 18. INTERACTIONS OF LIGHT AND MATTER
19. 19. Light and Matter Interactions Reflection  Absorption  Transmission  Scattering 
20. 20. Light and Matter Interactions Transparent  Translucent  Opaque 