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HSC Physics

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  1. Module 1: Kinematics
    1.1 Motion in a Straight Line
  2. 1.2 Motion on a Plane
  3. Module 2: Dynamics
    2.1 Forces
  4. 2.2 Forces, Acceleration and Energy
  5. 2.3 Momentum, Energy and Simple Systems
  6. Module 3: Waves and Thermodynamics
    3.1 Wave Properties
  7. 3.2 Wave Behaviour
  8. 3.3 Sound Waves
  9. 3.4 Ray Model of Light
  10. 3.5 Thermodynamics
  11. Module 4: Electricity and Magnetism
    4.1 Electrostatics
  12. 4.2 Electric Circuits
  13. 4.3 Magnetism
  14. Module 5: Advanced Mechanics
    5.1 Projectile Motion
  15. 5.2 Circular Motion
  16. 5.3 Motion in Gravitational Fields
    2 Topics
  17. Module 6: Electromagnetism
    6.1 Charged Particles, Conductors and Electric and Magnetic Fields
  18. 6.2 The Motor Effect
    1 Topic
  19. 6.3 Electromagnetic Induction
  20. 6.4 Applications of the Motor Effect
    1 Topic
  21. Module 7: The Nature of Light
    7.1 Electromagnetic Spectrum
    3 Topics
  22. 7.2 Light: Wave Model
  23. 7.3 Light: Quantum Model
    2 Topics
  24. 7.4 Light and Special Relativity
  25. Module 8: From the Universe to the Atom
    8.1 Origins of the Elements
    5 Topics
  26. 8.2 Structure of the Atom
    3 Topics
  27. 8.3 Quantum Mechanical Nature of the Atom
    2 Topics
  28. 8.4 Properties of the Nucleus
    2 Topics
  29. 8.5 Deep Inside the Atom
    4 Topics
Lesson 23, Topic 2
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The Photoelectric Effect

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The photoelectric effect is a phenomenon in which electrons are ejected from a metal when light is shone on the metal surface.

Electrons emitted in the photoelectric effect are known as photoelectrons.

K_{\text{max}}=hf-\phi

Inconsistencies with Wave Model

The classical (wave) model of light stipulated that the energy of light depended on its intensity. Therefore, it predicted that ANY frequency of light could induce the emission of photoelectrons given that it was of a substantial frequency.

This was proven to be incorrect through experimentation, which revealed that:

  1. No photoelectric effect is observed for a particular metal until the incident light is above a threshold frequency, no matter the intensity of the light.
  2. Above that threshold frequency, electrons are immediately released from the metal.
  3. The kinetic energy of the released electrons is depended upon the type of metal surface and the frequency of light incident on the surface.

These phenomena were unexplainable with the classical model of light.

Maximum Kinetic Energy vs. Frequency

Photoelectric Effect Minimum Kinetic Energy Versus Frequency
  • The lines are parallel as their gradients are equal to h
  • The x-intercepts, or threshold frequencies, are different for each type of metal
  • The y-intercepts, or the work functions, are different for each type of metal