Photoelectric Effect Flashcards
(12 cards)
What does the photoelectric effect demonstrate about light?
That light behaves as a particle, not just a wave—it arrives in discrete packets called photons, each with energy E=hf.
What did classical wave theory predict about the photoelectric effect?
That electrons should be emitted at any light frequency, given sufficient intensity (brightness). This was proven false.
What are photons?
Discrete packets (quanta) of light energy, with energy E=hf, where h=6.63×10−34 Js.
How is the kinetic energy of a photoelectron measured in experiments?
By increasing the stopping potential V_s (a reverse EMF) until no electrons reach the opposite plate: E_kmax = eV_s.
What is meant by ‘maximum’ kinetic energy in the photoelectric effect?
It refers to electrons emitted from the surface of the metal (not deeper layers), which have the most energy.
What is the photoelectric equation?
E_kmax = hf − ϕ
Where ϕ is the work function—the minimum energy to liberate an electron from the metal.
What is the threshold frequency?
The minimum frequency needed to emit electrons from a metal: f_threshold = ϕ/h.
What did the photoelectric effect prove about photons?
That a single photon can only eject one electron, regardless of intensity, confirming quantised energy transfer.
What was the goal of the Michelson-Morley experiment?
To detect Earth’s motion through the hypothesised aether by measuring changes in the speed of light due to Earth’s motion.
What setup did Michelson and Morley use?
An interferometer that split a light beam into two perpendicular paths, reflected them back, and recombined them to observe interference patterns.
What result did Michelson-Morley observe?
No shift in the interference pattern, no matter how the device was rotated—contradicting the aether theory.
What did the null result imply?
That the speed of light is the same in all directions—light does not need a medium, and absolute motion can’t be detected.
