Momentum

• 1916 Einstein extended the photon idea

• when light interacts with matter, not only energy but also linear momentum is transferred via photons

• momentum is also transferred in discrete amounts p=hf/c = h/? photon momentum

• E=hf = hc/? p=hf/c= h/?

• => E = pc

• recall that E2=p2c2 + m2c4 => m=0 massless

• short wavelength photons have more energy and momentum!

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