Flashcards in Particle Physics Deck (134)
Who first observed the photoelectric effect?
What is the photoelectric effect?
A metal can emit electrons if illuminated by electromagnetic radiation under specific conditions.
What does the photoelectric effect depend on?
What doesn't the photoelectric effect depend on?
What is the relationship between max kinetic energy of the emitted electrons and light intensity?
They are independent of each other.
What is the time delay between the light striking the metal and the first electrons being emitted?
There is no delay.
How is the photoelectric effect demonstrated?
-A metal plate is placed on top of a negatively charged golden leaf electroscope.
-If the EM radiation releases electrons, the metal will become positively charged.
-Electrons then move up the electroscope so the gold foil within will return to a vertical position.
Who developed the solution to the photoelectric effect problems?
Einstein and Planck
What were the three problems with the photoelectric effect?
-The ability of a metal to emit electrons didn't depend on intensity.
-The kinetic energy of the electrons is unaffected by the intensity.
-No time delay was observed.
What was Planck's theory regarding the photoelectric effect?
Energy was quantised (ie. discrete not continuous)
How did Einstein develop Planck's work on the photoelectric effect?
He showed that EM radiation could be considered as quanta of energy called photons.
What is a photon?
A quanta of electromagnetic radiation.
What has modern physics discovered about the properties of EM radiation?
It can also have particle like properties.
How is the energy carried by a photon calculated?
E = hf
E = hc / λ
What led to the theory of wave particle duality?
-Interference and diffraction can only occur with waves.
-The photoelectric effect can only occur with particles.
How are Joules converted into electron volts?
Energy in J = energy in eV x 1.60x10^-19
How are electron volts converted into Joules?
Energy in eV = energy in J / 1.60x10^-19
What is the energy carried by an EM wave dependent on?
Frequency or wavelength
In terms of the photoelectric effect, where do electrons within a metal sit?
In a potential energy well.
What is the work function of a metal?
The minimum energy required to remove an electron from the surface of a metal.
What happens when a photon collides with an electron in a metal?
The photon transfers all of its energy to the electron so the photon is absorbed.
How long does the absorption of a photon into a metal surface take?
The process is instantaneous.
How many photons can electron absorb?
An electron can only absorb one photon.
What is the threshold frequency?
The lowest of EM radiation that will emit electrons from the surface of the metal.
How is threshold frequency calculated?
fT = ϕ/ h
How is the maximum kinetic energy of a photoelectron calculated?
Ek = hf - ϕ
What does Ek represent?
Maximum kinetic energy
Why doesn't intensity affect the Ek of emitted electrons?
-hf remains constant
-More photons are emitted meaning more electrons are emitted but with the same Ek.
Why isn't there a time lag between the EM radiation striking the metal and the electron being emitted?
The energy from the photon is transferred instantly so the electron can escape instantly.