Photoelectric Effect Flashcards
What is the photoelectric effect?
Electromagnetic radiation shines of metal, metal absorbs some radiated energy
Some electrons may absorb enough energy to liberate them from their orbits.
Observation that UV can cause something to lose charges.
What are photons?
The idea that light is made up of individual units called photons
Light travels in small ‘bundles’ and has a certain amount of every associated with it, a ‘quantum’.
E = hf
Planck’s formula, showing how much energy in a given quantum
h = Planck’s constant, 6.63x10^-34 Js f = frequency of the beam of light E = energy of light emitted
What is intensity of light a measure of?
How MANY photons there are.
Does NOT depend on colour
Monochromatic
Light of a single frequency
Photoemission
Occurs when a photon of sufficient energy (a sufficiently high FREQUENCY) strikes a metal and an electron gains enough energy to overcome the weak attractive forces
Must be a reactive metal (weak attraction)
Therefore dim violet light will work but not bright red light
What is the work function
Then MINIMUM amount of energy needed to remove the electron
Y-int of a Ek vs f graph
Φ = hf0
f0 is min frequency required (threshold frequency)
Equation to find Ek max of an ejected electron
Ek = eV
e is charge on electron
V is stopping voltage (of photoelectric cell)
From W=Vq
hf = Φ + Ek
From the graph of Ek vs f
(If written in Y=mx+c form;
Ek = hf - Φ)
hf is the energy of the incident photon
Φ is the work function
Any leftover energy becomes the Ek of the ejected electron
Can be written as hf = Φ + eV
How does the intensity of the light affect Electrons emitted?
Greater intensity results in a greater number of electrons that fly off (more protons to knock off more electrons)
BUT does not affect Ek of emitted electrons (speed)
Frequency must be above the threshold frequency - an intense low frequency light will not eject electrons.
