11TH GRADE · QUANTUM PHYSICS
Photons and the photoelectric effect
Photon energy and momentum, photoelectric effect equation and red boundary.
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Basic Concepts
Photon
A quantum of electromagnetic radiation that transfers energy and momentum.
The photon has no rest frame and non-zero rest mass: its energy E = hν, and its momentum p = h/λ.
Photo effect
The emission of electrons by a substance under the influence of electromagnetic radiation.
One photon transfers energy to one electron: frequency determines the possibility of exit and the energy of the electron, intensity determines the number of electrons.
red photo effect border
The lowest frequency or longest wavelength at which the photoelectric effect is still possible.
Below the threshold frequency, the photoelectric effect will not begin even at very high light intensity.
Physical quantities
Photon energy
The energy of one quantum of electromagnetic radiation.
Unit: joule ·
Planck's constant
Coefficient of coupling between photon energy and frequency.
Unit: joule second ·
Emission frequency
The number of oscillations of the electromagnetic field per unit time.
Unit: hertz ·
Mass equivalent of photon energy
Ratio of photon energy to c²; this is not the rest mass, which is zero for a photon.
Unit: kilogram ·
Photon rest mass
The invariant rest mass of a photon is zero; the value E/c² is not the rest mass.
Unit: kilogram ·
Photon momentum
A measure of the translational motion of a photon.
Unit: kilogram-meter per second ·
Work function
Minimum energy to remove an electron from the surface of a substance.
Unit: joule ·
Photoelectron kinetic energy
The energy of motion of an electron after leaving a substance.
Unit: joule ·
Photoelectron mass
The mass of an electron emitted during the photoelectric effect.
Unit: kilogram ·
Electron charge modulus
Positive value of the modulus of the electric charge of an electron.
Unit: pendant ·
Holding voltage
The voltage at which the fastest photoelectrons stop reaching the anode.
Unit: volt ·
Threshold frequency
Minimum frequency of light for the photoelectric effect.
Unit: hertz ·
Red border by wavelength
The maximum wavelength of light that causes the photoelectric effect.
Unit: meter ·
Lesson formulas
Photon energy
The energy of a photon increases with frequency and decreases with wavelength.
Condition: For a photon in a vacuum; The rest mass of the photon is zero.
Mass equivalent of photon energy
The energy of a photon can be formally compared to a mass equivalent, but this is not the rest mass of the photon.
Photon momentum
The momentum of a photon is determined by its energy or wavelength.
Condition: For a photon in vacuum.
Planck's constant
Planck's constant sets the quantum scale of action.
Speed of light
The speed of light in a vacuum is approximately three hundred million meters per second.
Electronvolt to joules
One electron volt is equal to the charge energy of an electron when passing through a potential difference of one volt.
Einstein's equation for the photoelectric effect
The photon energy is spent on the work function and kinetic energy of the electron.
Photoelectron kinetic energy
The maximum kinetic energy is related to the speed of the electron and the retardation voltage.
Red limit for energy
At the red boundary, the photon energy is exactly equal to the work function.
Threshold frequency of photoelectric effect
The minimum frequency is determined by the work function and Planck's constant.
Red border by wavelength
The maximum wavelength is related to the speed of light and the threshold frequency.
Related formulas
The same formulas in the reference, with symbols and units.
Tasks on the topic
Statements, answer options and the walkthrough.