Chapter 13: Quantum Physics Flashcards
what is quantum physics
physics of everything very small using the quantum model
what is a quanta
a packet of energy
what did planck discover
light carries energy in packets.
The energy of the packet was dependent upon the frequency of the light
how does frequency of the light wave vary with energy of the quanta
higher the frequency the higher the energy in the packet
what is a photon
the specific packets that light carries energy in
how is the energy in the light expressed
as temperature so a higher temp means a higher average energy and higher frequency causing the light to glow
what are the two energy of a photon equations involving Planck’s constant
E = hf
Energy of a photon = Planck’s constant x frequency
E = hc/λ
Energy of a photon = (Plancks constant x Speed of light) / wavelength of light
what are h, f, c, λ measured in
h- Js
f- Hz
c- ms^-1
λ- m
what is an electronvolt
a miniscule amount of energy convenient when dealing with individual particles and photons
what is the energy of a photon equation involving an electronvolt
E = e x V
energy of a photon = elementary charge x (electronvolt or potential difference)
How do you convert between energy and electronvolts
eV –> J multiply by 1.6 x 10^-19
J –> eV divide by 1.6 x 10^-19
what is the energy gained by the particle equation
Q x V = 0.5 x m x v^2
charge x potential difference = 0.5 x mass x velocity squared
what is the photoelectric effect
electromagnetic radiation can be used to remove electrons from the surface of a metal
what two models can be used to demonstrate the photoelectric effect
electroscope
photocell
describe how the photoelectric effect works in an electroscope
> The electroscope is negatively charged repelling a gold leaf from the main rod
photons emitted from a source striking the metal cap
when photons of a correct frequency strike the metal there is enough energy to dispell the electrons
once the electrons are emitted the electroscope becomes neutral so the leaf is no longer repelled
describe how the photoelectric effect works in a photocell
> a potential divider circuit is setup with a photocell connected
photons are emitted at the photocell
when photons of the correct frequency strike the photocell electrons are emitted from a positive electrode inducing a current
what is the work function
minimum energy required to free an electron from a specific metal
what is threshold frequency
the minimum frequency of an incident ray that will free the electrons from the surface of a specific metal
what is the KEmax equation
KEmax = h x f - φ
maximum kinetic energy of a photon = plancks constant x frequency of light wave - work function
what is the effect of light intensity on the photoelectric effect
greater intensity means more photons hit surface per second so more electrons are emitted per second
what happens to an electron when the incident ray has a frequency lower than the threshold frequency
the electron is not dispelled
what happens to an electron when the incident ray has a frequency equal to the threshold frequency
the electron is emitted with no KE
what happens to an electrons when the incident ray has a frequency greater than the threshold frequency
the electron is emitted with kinetic energy
what did prince louis de Broglie state
electrons exist as both waves and particles
what is the de broglie wavelength
the wavelength of an object that acts as a particle and a wave
what is the de broglie wavelength equation
λ = h / p
de broglie wavelength = plancks constant / momentum
what is Thermionic emission
when a hot cathode emits electrons
how can you increase thermionic emission
increase the potential difference in the cathode
