Presentation on theme: "The Photoelectric Effect Waves as particles? What, are you crazy??"— Presentation transcript:
The Photoelectric Effect Waves as particles? What, are you crazy??
What is the Photoelectric Effect? When light is shone on a metal, electrons are ejected from the metal. The ejected electrons have a certain amount of kinetic energy.
Explain. According to wave theory, the energy of a wave is directly proportional to its amplitude. With light, the higher the amplitude, the brighter (more intense) the light. Therefore, brighter (more intense) light, which has higher amplitudes, should pop off electrons with more kinetic energy than dimmer light (lower amplitude). NOT THE CASE
Instead Only certain frequencies of light causes electrons to be ejected (such as blue), while others (such as red) did not. The brightness of the blue light has no effect on the KE of the electrons ejected.
Instead Once electrons are ejected, the brightness of the blue light only effects the number of electrons ejected, not the KE of those electrons.
What is going on? Max Planck (1900) First to suggest a relationship between the energy and frequency of a wave. Objects give off different frequencies of light depending on their temperature. Proposed that objects do not emit energy continuously, but rather in small, specific amounts called quanta. Also proposed that the amount of energy associated with a light wave is directly proportional to its frequency (not its amplitude) E = hv h = x Js
How does this explain the photoelectric effect? This is where Einstein comes in (1905) Light as particles, each with its own quantum (specific amount) of energy, depending on its frequency. He called these particles photons. Electrons are only ejected from the metal if the photon hitting the metal has the minimum amount of energy needed to eject an electron. (compare blue and ultraviolet to red)
The frequency of the photon is what effects the energy of the ejected electrons. Brightness of light is therefore related to the number of photons present, not the energy of those photons. That is why brightness of light only effects the number of electrons ejected, not the energy of those electrons.
Einstein wins Nobel Prize!! Summary Energy is absorbed an released in quanta, not continuously Photoelectric effect hints to the particle nature of light. Particles of light are called photons. The energy of each photon is directly proportional to its frequency. Ability to eject electrons from a metal depends on the frequency of the photons hitting the metal, not on the brightness of the light. Only photons with the minimum amount of energy needed to eject and electron will do so. Then, increasing the brightness increases the number of electrons ejected. Since different metals hold on to their electrons more or less tightly, different metals require different minimum energies to eject those electrons