Quantum Physics Flashcards
What is meant when we refer to the speed of light?
The speed that all photons travel at in a vacuum, which is independent of frequency.
What is the charge of a photon.
Photons have no charge.
What does the energy of a photon depend upon?
Frequency. Nothing else.
What power of ten best represents the gaps between atoms?
-10
How do you calculate the number of photons of light emitted by a source per second?
Number of photons per second = Power x % of power emitted in valid region of EM spectrum / Energy of one photon
State what is meant by photoelectric effect.
The emission of electrons from the surface of a metal when electromagnetic waves (of frequency greater than the threshold frequency) are incident on the metal.
Electromagnetic radiation is incident on a negatively charged zinc plate. Electrons are emitted from the surface of the plate when a weak intensity ultraviolet source is used. Electrons are not emitted at all when an intense visible light from a lamp is used.
Explain these observations.
Photon(s) mentioned
One-to-one interaction between photons and electrons
Energy of photon is independent of intensity / intensity is to do with rate (of photons / photoelectric emission) / photon energy depends on frequency / energy of photon depends on wavelength / photon energy frequency / photon energy 1/
energy of uv photon(s) > work function (of zinc) / frequency of uv > threshold frequency
The photoelectric effect cannot be explained in terms of the wave-model of electromagnetic waves. Discuss how the new knowledge of the particulate nature of radiation was used by physicists to validate the photon model.
The wave model cannot explain there is a threshold frequency for models.
The new model/photon model proposed one-to-one interaction between photons and electrons and this successfully explained why threshold frequency exists.
Energy of photon (hf) must be greater than or equal to the work function of metal.
The kinetic energy of emitted electrons was independent of the incident intensity.
What is the electron-volt?
The energy gained or lost by an electron when it moves through a voltage of 1 volt.
What is the work function?
The smallest amount of energy needed to eject an electron from an atom.
What is the threshold frequency?
The frequency below which, the photons do not have enough energy to eject an electron.
What is meant by the de Broglie wavelength of an electron?
Electrons are observed to behave as waves where the electron wavelength depends on its speed.
