Photoelectric effect
Knock electrons out with light and tell apart the roles of frequency and intensity.
The energy of a single photon is determined by its frequency. Photoelectrons are emitted only when hf is at least the work function; above the threshold, raising the frequency increases the maximum initial kinetic energy, while raising the intensity mainly increases the number of electrons emitted per unit time.
Max kinetic energy vs. frequency
No photoelectrons below the cutoff frequency; intensity does not change the maximum kinetic energy.
Think about it
If the incident light is below the cutoff frequency, can raising the intensity alone produce photoelectrons?
No. Each photon's energy hf is still less than the work function; raising the intensity only increases the number of low-energy photons.
Model assumptionsMonochromatic light · Clean metal surface · h = 4.136×10⁻¹⁵ eV·s · Interactions between photoelectrons neglected · Number emitted is illustrative only
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.