lecture27

# lecture27 - Physics 2102 Gabriela Gonzlez Particles and...

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Particles and waves Physics 2102 Gabriela González

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Light is a wave We observe diffraction for waves going through apertures, and interference when waves add to each other. Young performed his “double slit” experiment in 1801 to decide whether light was a particle (like Newton said) or a wave.
Electrons are particles JJ Thompson, in 1897, proved that cathode rays were made of negatively charged particles: electrons ! The deflection due to an electric field proved the charge was negative. Using an electric and magnetic field so that the beam was undeflected, he found the velocity of the beam (v=E/B, up to ~c/3 in high vacuum!) Measuring the deflection of the beam in the absence of the magnetic field : the vertical deflection d can be measured, and is equal to d=1/2 a t2 = ½ (qE/m)(L/v), so he could derive e/m : the same for all cathode rays, for all velocities: cathode rays were made of particles. Also, e/m ~1,700 larger than for a H atom: particles were “sub atomic”. JJ Thomson won the Nobel prize for this in 1909. The charge of the electron (the proof that charge was quantized) was measured in by Millikan with an oil-drop experiment. He won the Nobel prize for this in 1923.

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Electromagnetic energy is quantized At room temperature, black bodies emit mostly infrared wavelengths, but as the temperature increases, black bodies start to emit visible wavelengths, appearing red, orange, yellow, white, and
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## This note was uploaded on 11/18/2011 for the course PHYSICS 2102 taught by Professor Dowling during the Fall '10 term at LSU.

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lecture27 - Physics 2102 Gabriela Gonzlez Particles and...

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