Photons, not a spreading wave
"Photons, not a spreading wave" is a free, interactive Class 12 Physics simulation for NEET and JEE, built on the NCERT section "Where the wave picture fails" in Dual Nature of Radiation and Matter. Light on a metal surface as photons, each freeing at most one electron, with a wave-picture toggle that predicts slow build-up and emission at any colour. NEET has asked about this idea 5 times in 10 years of papers. JEE Main asked 40 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Where the wave picture fails in Dual Nature of Radiation and Matter. Change the values and watch what happens.
What it shows
NCERT §11.4.3, §11.5
Light on a metal surface as photons, each freeing at most one electron, with a wave-picture toggle that predicts slow build-up and emission at any colour.
Controls
4 to try
- Sliderwavelength 200–750 nm
- Sliderintensity 0–100%
- Segmentedmetal Cs / Na / Zn / Cu
- Togglephoton picture / wave prediction
Try this
Show the brightest red light frees nothing from zinc, then find the longest wavelength that just frees electrons from caesium (≈580 nm)
Common mistake
Expecting very intense red light to eject electrons, or a delay before emission in dim light.
In NEET
10 years of papers
Asked 5 times in 10 years of NEET.
See the past questions: Photoelectric Effect, Dual Nature of Radiation and Matter (chapter)
In JEE Main
42 shifts analysed
40 questions from Dual Nature of Radiation and Matter across the 42 JEE Main shifts Lumi has analysed (2017–2026).
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.
Questions
5 answers
- What does the "Photons, not a spreading wave" simulation show?
- Light on a metal surface as photons, each freeing at most one electron, with a wave-picture toggle that predicts slow build-up and emission at any colour.
- What mistake does the "Photons, not a spreading wave" simulation fix?
- A common mistake it clears up: expecting very intense red light to eject electrons, or a delay before emission in dim light.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 5 times in 10 years of papers.
- Does JEE Main ask questions from Dual Nature of Radiation and Matter?
- Yes. JEE Main asked 40 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Where the wave picture fails" in Dual Nature of Radiation and Matter (Class 12 Physics).
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