Simulation · Physics · Class 12
Photons, not a spreading wave
From the lesson Where the wave picture fails in Dual Nature of Radiation and Matter. Change the values and watch what happens.
Photons, not a spreading wavePhysics · Class 12
The idea behind it
NCERT §11.5
- By the end of the nineteenth century the wave theory explained interference, diffraction and polarisation well. In it, light is an electromagnetic wave whose energy is spread continuously over the whole region the wave fills.
- On the wave picture, electrons at the surface soak up energy continuously. Brighter light has larger electric and magnetic field amplitudes, so each electron should gain more energy, and Kmax should rise with intensity. Experiment says it does not.
- Also on the wave picture, a strong enough beam of any frequency, shining long enough, should give electrons enough energy to escape. There should be no threshold frequency. Experiment says there is one.
- The wave spreads its energy over the whole wavefront, shared among a very large number of electrons, so each one gains energy only slowly. Calculations suggest that one electron could need hours or more to collect the work function.
- That clashes with observation (iv): emission is instantaneous. The wave picture fails on observations (i), (ii), (iii) and (iv) alike: it cannot explain the basic features of photoelectric emission.