3.2 - more about the photoelectric effect Flashcards
what is the U.V. catastrophe
where the measurements of radiation waves from an object at constant temp showed he waves intensity varied with wavelength
- the theory of electromagnetic waves predicted UV light to have infinite intensity
Whi solved the U.V. catastrophe
-how
Plank
- stating energy of each vibrating particle must be quantized
E=hf
h - planks constant, energy can only be in multiples of a certain amount
Who solved the photoelectric effect
-how
Einstine
- updated the wave theory radiation stating electromagnetic waves consists of photons (wave packets of energy)
What did Einstine and planks ideas prove
that energy is quantised
Define work function
the min amount of energy needed by an e- to escape from the surface of the metal when the metal has 0 potential
What happens to an e- in metal if it exceeds the work function
it leaves the metal becoming a photoelectron
What happens to an e- in metal if it doesn’t exceed the work function
it gains Ek but collided with outher e-/ +ve metal ions, loosing all the energy before it can leave the surface
Vacuum photocell
-diagram and description
What are photocells used for
to calc the Ek (max) of photoe- from a given light frequency
Describe intensity
the energy of energy carried per sec by the incident ray
(more photons per sec)
What is intensity proportional to
-why
photoelectric current
Increases intensity = more photons per sec = more e- that absorb the photons overcoming the metal’s work function = more e- to carry the charge to generate
Q=It
Q= e- charge
Give the equation used to calc the no. of photoe- produced per sec
No. = I / e
e= electronc charge
what does intensity not effect
- why
the Ek (max)
- since each e- is absorbing only 1 photon, E=hf per photon, so more are removed but with the same energy absorbed
Give the graph and equation from the vacuum photocell
y = mx + c
Ek(max) = hf - Ø
h = gradient, constant for all graphs.
