- The equation that relates the frequency, wavelength, and speed of a light wave-- frequency=c / wavelength--can be rewritten as c=frequency x wavelength . A friend who knows mathematics but not much astronomy or physics looks at this equation and says: "This equation tells me that the higher the frequency, the greater the wave speed c. Since visible light has a higher frequency than radio waves, this means that visible light goes faster than radio waves." How would you respond to your friend?
All electromagnetic radiation travels at the same speed--c. So as the frequency goes up the wavelength goes down.
- What is a blackbody? In what way is a blackbody black? If a blackbody is black, how can it emit light?
A blackbody is black in that it absorbs all frequencies of light. Room temerature objects that appear black to us visually are emitting in the infrared--so they absorb the visible and re-emit in a region of the spectrum that we can't see.
- Your body temperature is 98.6o F. What kind of radiation do you predominantly emit? At what wavelength do you emit the most radiation?
l=.0029/T
Tcentigrade=5/9 (TF-32)=37oC
TK=TC+273=310oK
l=9.35 micrometers and this is in the infrared region
- The human eye is most sensitive over the same wavelength range at which the Sun emits the greatest intensity of radiation. Suppose creatures were to evolve on a planet orbiting a star somewhat hotter than the Sun. To what wavelength would their eyes most likely be sensitive?
Their eyes would be sensitive to the blue/violet (or possibly ultraviolet) portion of the spectrum--depending on how hot the star was.
- Why do you suppose that ultraviolet light can cause skin cancer but ordinary visible light does not?
The energy of a photon is proportional to its freqeuncy. The higher the frequency, the more energetic the photon. Destruction of cell components (or any type of destruction for that matter) is due to energy deposition. Higher energy photons can deposit more energy in a cell and hence cause more damage.