Ch 11 covers the dual nature of light and matter — the photoelectric effect (Einstein), photon properties, de Broglie hypothesis, and the Davisson-Germer experiment confirming electron waves.
Light ejects electrons from metal surface. Observations: (1) instantaneous — no time delay, (2) KE depends on frequency not intensity, (3) below threshold frequency, no emission regardless of intensity. Einstein's equation: KE_max = hf − φ (φ = work function). Stopping potential eV₀ = hf − φ. Light behaves as particles (photons) with E = hf, p = h/λ.
de Broglie hypothesis: all matter has wave nature. λ = h/p = h/mv. For electron accelerated through V: λ = 1.23/√V nm. Davisson-Germer experiment: electron beam diffracted by nickel crystal — confirmed wave nature of electrons. Heisenberg uncertainty: Δx·Δp ≥ h/4π. Applications: electron microscope (smaller λ → better resolution).
Download: https://ncert.nic.in/textbook/pdf/leph203.pdf | Part II: https://ncert.nic.in/textbook/pdf/leph2ps.zip
Wave theory predicts: (1) any frequency should eject electrons given enough intensity, (2) there should be a time delay for low intensity, (3) energy should depend on intensity, not frequency. Experiments showed the opposite — there is a threshold frequency, emission is instant, and KE depends on frequency. Only Einstein's photon model (E = hf) explains all observations.
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