Conceptual Physics

(Sean Pound) #1

It was not easy for scientists to accept Einstein’s new theory. When four elite scientists
í including Planck í nominated Einstein to the Prussian Academy of Science they
wrote, “That he may have missed the target in his speculations, as, for example, in his
hypothesis of light quanta, cannot really be held too much against him, for it is not
possible to introduce fundamentally new ideas, even in the most exact sciences, without
occasionally taking a risk.”


One year later, the American physicist Robert A. Millikan reported a precise
confirmation of Einstein’s equation for the energy of the photon, E = hf.


Photon


Packet of energy
·Light is quantized
·Brighter light = more photons

Energy of a photon


E = hf


E = energy


h = Planck’s constant


f = frequency


Constanth = 6.63×10í^34 J·s


What is the energy of this photon


of red light?


E = hf


E = (6.63×10í^34 J·s)( 4.41×10^14 sí^1 )


E = 2.92×10í^19 J


Copyright 2007 Kinetic Books Co. Chapter 36^663

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