Photoelectric effect, photons, Planck’s hypothesis

1. Wave-Particle Duality

1. Proposed to explain the dual nature of light and electromagnetic radiation.
2. Light exhibits both wave-like and particle-like properties.
3. Wave nature: Demonstrated by interference and diffraction.
4. Particle nature: Demonstrated by the photoelectric effect.

2. Photoelectric Effect

1. Discovered by Heinrich Hertz and later explained by Albert Einstein.
2. When light strikes a metal surface, it ejects electrons from the surface.
3. Ejected electrons are called photoelectrons.
4. Occurs only when the light has a minimum frequency (threshold frequency).
5. Einstein's explanation used the concept of photons, or light quanta.
6. The kinetic energy of the photoelectrons depends on the frequency of light, not its intensity.
7. Forms the basis of many devices, such as photoelectric cells and solar panels.

3. Photons

1. A photon is a quantum of electromagnetic radiation.
2. Photons are massless particles and always travel at the speed of light in a vacuum.
3. The energy of a photon is given by the formula: E = hν, where h is Planck’s constant and ν is the frequency of light.
4. The momentum of a photon is given by p = E/c, where c is the speed of light.
5. Photons are responsible for interactions in electromagnetic phenomena.

4. Planck’s Hypothesis

1. Proposed by Max Planck to explain blackbody radiation.
2. States that energy is emitted or absorbed in discrete quanta or packets.
3. The energy of each quantum is directly proportional to its frequency.
4. Formula: E = hν, where h is Planck’s constant (6.626 × 10⁻³⁴ Js).
5. Revolutionized the understanding of energy and quantum mechanics.

5. Applications

1. Used in photovoltaic cells to convert sunlight into electricity.
2. Forms the basis of quantum theory and modern physics.
3. Photoelectric effect is critical in digital imaging and optical sensors.
4. Helps in understanding phenomena like Compton scattering and electron microscopy.

6. Key Takeaways

1. Wave-particle duality bridges the classical and quantum views of light.
2. The photoelectric effect validated the particle nature of light.
3. Planck’s hypothesis laid the foundation for quantum mechanics.
4. Photons are central to understanding light-matter interaction.