Planck and Photoelectric Effect Flashcards
(9 cards)
What is a black body?
A black body is an object that absorbs and emits radiation at all wavelengths. It is an ideal emitter and absorber of electromagnetic radiation.
What did wave theory predict about radiation at short wavelengths?
Wave theory predicted that as the wavelength decreases, the intensity of emitted radiation should increase without limit, especially in the ultraviolet region.
What is the ultraviolet catastrophe?
It’s the failure of classical wave theory to explain black body radiation — specifically, the prediction of infinite UV intensity, which did not match experimental evidence.
How did Planck resolve the ultraviolet catastrophe?
Planck proposed that EM waves are emitted in discrete energy packets called quanta, with energy given by: E=hf where h is Planck’s constant and f is frequency.
What is the photoelectric effect?
It is the emission of electrons from a metal surface when light of a certain frequency shines on it.
Why couldn’t wave theory explain the photoelectric effect? (Reason 1)
Wave theory predicted that any frequency of light should eventually cause emission, since energy would build up over time. But experiments showed a threshold frequency is required.
Why couldn’t wave theory explain the photoelectric effect? (Reason 2)
According to wave theory, electrons should take time to absorb energy, but photoelectric emission is immediate, which contradicts the theory.
Why couldn’t wave theory explain the photoelectric effect? (Reason 3)
Wave theory suggests increasing intensity increases energy per electron, but actually it only increases the number of photoelectrons emitted — not their individual energy.
Why couldn’t wave theory explain the photoelectric effect? (Reason 4)
Photoelectrons are emitted with a range of kinetic energies, which is inconsistent with wave theory predicting gradual energy build-up.
