Unit 2 - Photons and Quantum Physics Flashcards
What is a photon?
A quantum/packet of light (or energy idk)
What is an electron volt
the unit of energy equal to the work done when an electron is moved through a potential difference of 1 volt.
1 eV = 1.6x10⁻¹⁹ Joules
What is the photoelectric effect?
Electrons can escape from the surfacec of certain metals if the surface of the metal is hit by the electromagnetic radiation (such as light) of sufficient frequency
What are the 4 laws of photoelectric emission?
1) The number of electrons released from the surface is proportional to the intensity of the incident radiation
2) Emission occurs with no observable time lag.
3) The kinetic energy of the photoelectrons depends only on the frequency of the light and NOT on the intensity of the light.
4) There exists a threshold frequency of emission. When frequency is less than the threshold frequency, no photoelectrons sare emitted. Threshold frequency depends on the type of metal.
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(so baisicaly the threshold frequency is like a requirement type thing, and the frequency must be that or greater so the electrons can be emitted).
Explain how the photoelectric effect works
The photons penetrates into the surface layer of the metal and imparts all of its energy to one electron in the material . Only 1 photon can interact with 1 electron. The intensity of light is proportional to number of photoelectrons. The electrons need a certain amount of energy to be released from the metal to gain zero energy. This is known as the work function of the metal.
(this is why there is a need for a threshold frequency)
In photoelectric emission, if the photon has more than the minimum energy what can be observed?
The difference between the minimum energy and the photon’s energy is seen as kinetic energy of the photoelectron. This obeys the law of conservation of energy.
Define the work function (φ)
the minimum energy required to release an electron from the surface of a metal.
Symbol (φ) smth like that
What is the threshold frequency
the minimum frequency of light required to release an electron from the surface of a metal.
What is a vaccume photocell
a device which can be used to measure the maximum kinetic energy of electrons.
What is a wave phenomenon
when laser light is passed through a diffraction grating a line of dots are obtained of the screen corresponding to the orders where constructive interference is seen.
How do u demonstrate the photoelectric effect?
using a gold leaf electroscope
ion really know how it works
Equation for energy and how to derive
E = hc/λ
Given equations: e=hf and c= fλ
Rearange to f = c/λ
Substitute to e = hc/λ
Energy = planks constant x speed of light / wavelength
Describe visible light colours and nanometers
Red-700
Orange-650
Yellow-600
Green-550
Blue-500
Indigo-450
Violet-400
What are wavelengths for EM spectrum (m)
Radiowaves - 10³-10⁰
Microwaves -10⁻²
Infrared - 10⁻³
Visible light - 10⁻⁶
Ultraviolet - 10⁻⁸
X-rays - 10⁻⁹
Gamma-rays - 10⁻¹⁰-10⁻¹²
(These are measurements in meters)
How is absorption spectra obtained
By passing continuous spectra through a cold gas
