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VISUAL PHYSICS ONLINE 7.1 THE NATURE OF LIGHT
ELECTROMAGNEITC WAVES P71 000 (A) Describe the experiment used by Hertz and his observation of the photoelectric effect. What did he do about these observations? (B) Describe how Einstein used the ideas of Planck to explain the photoelectric effect. View solution below only after you have completed the answering the question. |
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Solution
A high voltage applied to an induction coil produced sparks in the gap. The induction coil acted as a transmitter that emitted electromagnetic radiation which included radio waves and UV radiation. When a sheet of glass was placed between the transmitter and receiver, the spark in the receiver was weaker due to the absorption of the UV by the glass. Hertz noted the observation but did not follow it up. The UV absorbed by the metal receiver enabled electrons to
be emitted more easily giving a bigger spark – photoelectric effect. (B) Planck ·
Energy of atomic oscillators is quantized DE = h f Einstein ·
Particle model for light – light consisted of
photons – energy of each photon hf ·
An electron emitted immediately from the surface by
the interaction with a photon Applied the Law of Conservation of Energy Energy of incident photon = Energy to release electron from surface + KE of ejected electron h f = ½ m v2 + f = ½ m vmax2 + W W is the min energy needed to remove an
electron from the surface – work function For
electron to be released h f
³ W threshold
frequency h fc = W |
