PLANET EARTH

LIGHT

Lab Experiments

• Distance Behavior - I = A/r2 +B

• Definition of color - The ratio of two colors at the same distance.

• Color and Temperature - objects get more “blue” with increasing temperature.

• Attenuation I = I0• e-•d

Source• Observations - visible

– for Hydrogen– 1/ = R(1/22 - 1/n2) , R = 1.097 •10-7 m-1

– n = 3 red light = 6562 •10-10

– n = 4 blue light = 4861 •10-10

– This is an empirical formula!– Each atom has a unique spectrum!– Formulas like this, give the colors of light that

come out of atoms.

Bohr Model• Quantized energy levels exist in all atoms.• For Hydrogen the energy of each level is

– En = 13.6/n2

• Transitions between levels either absorb or release energy. Energy is released in the form of light packets or photons each of energy:– E = hc/ = hf Einstein postulates this for PE effect– the energy available is the difference between the two

levels involved in the transition.

• This is consistent with the “observations” on the previous slide.