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The groundbreaking discoveries in physics by j.j. Thompson, max planck, and albert einstein. Thompson measured the charge to mass ratio of the electron, leading to the discovery of electrons as negative charges much smaller than atoms. Blackbody radiation, as described by stefan's law and wien's law, explains how hot objects emit electromagnetic radiation. Planck's quantum hypothesis introduced the concept of quantized energy, and einstein's photoelectric effect demonstrated that light behaves as both a particle and a wave.
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Properties of the Electron
J.J. Thompson (1897) measured the charge to mass ratio of the electron (cathode rays)
1.76x10 C/kg B r
m
e (^11)
E-electric field, B-magnetic field, r-radius of curvature Electrons are negative charges but are much smaller in mass than atoms
Millikan’s oil drop experiment: found e=1.6x10-19^ C Electric charge in atoms are quantized
Blackbody Radiation, Wien’s Law
Hot objects emit electromagnetic (EM) radiation (waves) with EM Intensity~T^4 – Stefan’s Law Blackbody: Absorbs all EM radiation incident on it Blackbody radiation: EM radiation emitted by a blackbody resulting from its interior temperature Examples: stars (sun), red hot metal block, fire embers
Wien’s Law for Blackbody Radiation: Peak wavelength in blackbody radiation spectrum inversely proportional to temperature:
OR peak frequency is proportional to temperature:
f (^) peak =(5.88x10^10 s -1^ K-1^ ) T
Radiant energy from intensity spectrum of blackbody equals area under curve.
Blackbody EM radiation results from oscillating electric charges on molecules within blackbody.
The Photoelectric Effect
Einstein’s Photoelectric Effect (Nobel Prize-1921)
hf V e e
