Physics 2. Chapter 27 Sections 1-3. Blackbody Radiation Curve. All objects emit EM radiation Usually consists of a continuous distribution of λ As temp increases the more the max intensity shifts to shorter λ
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Classical physics predicts that as λ approaches 0 the amount of energy radiated should become infinite
Instead data shows that as λ approaches 0 the amount of energy radiated also approaches 0
Blackbody is a hollow object with a small opening through which light can enter
Energy gets absorbed every time light hits the wall inside
If box is insulated the energy absorbed causes the temp inside to rise
Energy will be radiated inside the box and some will escape
E = nhf
where n=quantum # (0,1,2…), f=frequency of resonator, h=Planck’s constant = 6.63 x 10-34 Js
The idea was so radical that even Planck didn’t think it was realistic. It was just a mathematical model.
Classical physics says:
EM waves are composed of photons
Each photon has an energy, E, given by E = nhf that can be absorbed by an electron
Einstein says that if light hits a metal it can do 1 of 2 things:
If photon has more energy than hft the rest goes into KE of ejected electron
photon E = energy to remove electron (work fn) + max KE of ejected electron
hf = hft + KEmax
If f < ft then no ejected electrons
KE only depends on f not intensity (increase in intensity means more ejected electrons but at same KE)
Slope is h (Planck’s constant)
The work function for a silver surface is 4.73 eV. Find the minimum frequency that light must have in order to eject electrons from its surface.
Compton struck an electron at rest with an xray photon
Noticed scattered photon has a frequency that is less than the incident frequency
Difference between the 2 frequencies depended on the angle at which the scattered photon left
This phenomenon became the basis for the idea of wave-particle duality.