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Dual Nature of Radiation and Matter — Revision Notes

NIOS · Class 12 · Physics

Dual Nature of Radiation and Matter revision notes for NIOS Class 12 Physics: 4 topics in quick points. Part of the NIOS Class 12 Physics syllabus.

45 questions30 flashcards14 formulas & key relations5 concepts

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A labeled diagram of the experimental arrangement used to study the photoelectric effect, including the evacuated quartz tube, emitter plate, collector plate, incident light, variable voltage source,
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Key Topics to Revise

1

Photoelectric Effect — Discovery and Observations

  • Photoelectric effect was discovered by Hertz in 1887 while studying electromagnetic waves. He noticed that ultraviolet light made a spark gap conduct better.
  • Lenard (1900) confirmed that electrons are emitted from metal surfaces when light of sufficiently high frequency falls on them.
  • The emitted electrons are called photoelectrons.
2

Laws of Photoelectric Emission

  • Law 1 — Effect of Frequency on Maximum Velocity: The maximum velocity (and hence maximum kinetic energy) of photoelectrons INCREASES with INCREASE in frequency of incident light. It also depends on th
  • Law 2 — Intensity does NOT affect Maximum Velocity: The maximum velocity of photoelectrons is INDEPENDENT of the intensity of incident light. Doubling the intensity does NOT increase the speed of any
  • Law 3 — Threshold Frequency: For every material, there exists a minimum threshold frequency ν₀ below which NO photoelectrons are emitted, no matter how intense the light.
3

Einstein's Theory of Photoelectric Effect

  • Einstein proposed in 1905 that light is made of discrete bundles of energy called PHOTONS (quanta of light).
  • Each photon carries energy E = hν, where h is Planck's constant (6.626 × 10⁻³⁴ Js) and ν is the frequency of light.
  • Photons travel at the speed of light and have zero rest mass.
4

Solved Numerical Examples on Photoelectric Effect

  • EXAMPLE 1 (NCERT type): Sodium has work function φ₀ = 2.3 eV. Light of wavelength λ = 5×10⁻⁷ m is incident on it.
  • STEP 1 — Find Threshold Frequency: ν₀ = φ₀/h = (2.3 × 1.6×10⁻¹⁹) / (6.6×10⁻³⁴) = 3.68×10⁻¹⁹ / 6.6×10⁻³⁴ = 5.6×10¹⁴ Hz
  • STEP 2 — Find Energy of Photon: E = hc/λ = (6.6×10⁻³⁴ × 3×10⁸) / (5×10⁻⁷) = 1.98×10⁻²⁵ / 5×10⁻⁷ = 3.96×10⁻¹⁹ J

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Full Notes

Key Concepts

The photoelectric effect is the emissionWhen the collector plate AEvery metal has a characteristic minimumIn 1905A photoelectric tube (phototube) is

Frequently Asked Questions

What are the important topics in Dual Nature of Radiation and Matter for NIOS Class 12 Physics?
Key topics in Dual Nature of Radiation and Matter include Photoelectric Effect — Discovery and Observations, Laws of Photoelectric Emission, Einstein's Theory of Photoelectric Effect, Solved Numerical Examples on Photoelectric Effect. Study these first, then practise questions on each for the NIOS Class 12 board exam.
How should I revise Dual Nature of Radiation and Matter for the NIOS Class 12 board exam?
Learn the core ideas first, then work through the 45 practice questions on Dual Nature of Radiation and Matter. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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