1. The Science of Light
Group 9 presentation

2. Transparent, Translucent, and Opaque Objects
Objects can be described based on the amount of light allowed to pass through the object.
Transparent objects allow light to completely pass through. (glass, air, water)
Translucent objects partially allow light through with some light distortion. (stained or frosted glass, some plastics)
Opaque objects can reflect light or absorb it, but do not allow light to pass through. (wood, stone, mirrors)

3. Think of transparency as letting light from behind an object pass to reach your eye.
This makes the physics easier to understand than letting your eye see behind it.
Transparent
Translucent
Opaque

4. Some factors that determine transparency
Abundance and mobility of free electrons: Electrons absorb photons, or light, so it decreases transparency.
Structure of molecules composing a substance: Molecules farther apart than visible wavelengths of light will let it pass through.
How homogeneous the substance is: Less difference in media means less bending of light. Too much refraction will prevent the light from escaping.

5. How electrons cause opacity.
Electrons of lower energy absorb light to become electrons with higher energy. This causes the opacity of an object, and it also explains how light can be converted into electrical energy.
e- + E(light) -> e-

6. How distance, or bond length, causes transparency
Bond length is the distance between the nuclei of two bonded atoms.
Wavelength in this case is shorter than bond length, so light can pass through the substance.
Bond Length
Wavelength

7. How homogeneity affects transparency
The more uniform a substance's composition is, the less refraction it causes, and therefore the less opaque it is.
Relatively Heterogeneous Relatively Homogeneous

8. Greenhouse Effect

9. The Greenhouse Effect
Sunlight in the visible spectrum hits the inside of a car and gets absorbed into any surface it hits.
This causes the surface to heat up and emit infrared radiation, which is, in turn, absorbed by CO2 and other greenhouse gases.
This increases the temperature of the car to a temperature to a higher degree than the outside.

10. The Greenhouse effect part 2
As heat radiates off the inside of a car and gets trapped, the heat can get to extreme temperatures.
This can cause serious issues if anything is left alive in the car, so make sure all living beings are properly “dealt with” before leaving your car, even if you leave for only a few minutes.

11. Penumbras, Umbras, & Eclipses

12. Penumbra: when the sun’s rays are partly blocked, causing semi-darkness
Umbra: when the sun’s rays are completely blocked, causing total darkness

13. Solar and Lunar Eclipses
Solar Eclipse
Earth passes through the moon’s shadow
Lunar Eclipse
The moon passes through Earth’s shadow

14. Sources
Arizona Board of Regents. The Life Cycle of the Photon.
Net Industries. Color - Transparent, Translucent, And Opaque. Retrieved from
Richard W. Pogge (2010 June 3). Lecture 9: Eclipses of the Sun & Moon. Retrieved from
Scientific American. What determines whether a substance is transparent? For instance, why is silicon transparent when it is glass but not when it is sand or a computer chip? Retrieved from
UCSB Science Line. Why is the inside of a car hotter than the outdoor temperature on a sunny summer day? Retrieved from