Study Guides/Physics/Planck's Quantum Theory
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What is Planck's Quantum Theory?

Before the year 1900, scientists believed that light and heat (electromagnetic radiation) traveled as a continuous, unbroken wave. However, this theory failed to explain certain phenomena. Enter Max Planck, who changed physics forever with his Quantum Theory.

Question (Click to Flip)

What is Planck's quantum theory?

Answer

Planck's quantum theory states that radiant energy is emitted or absorbed not continuously, but in small, discrete packets called 'quanta' or 'photons'. The energy of each quantum is directly proportional to its frequency (E=hν).

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Key Facts

Core Idea: Energy travels in tiny packets, not as a continuous wave.

Name of packet: Quantum (or Photon for light).

Formula: E = hν.

Inventor: Max Planck (won the Nobel Prize in Physics in 1918).

The Main Postulates of Planck's Theory

In 1900, Max Planck proposed a revolutionary idea:

  1. Energy is Discrete, Not Continuous: Radiant energy (like light or heat) is not emitted or absorbed in a continuous, flowing wave. Instead, it is emitted in small, individual, discontinuous packets of energy.
  2. The Quantum: Planck called each of these small packets of energy a 'Quantum' (plural: Quanta). When talking specifically about light, a quantum of light is called a 'Photon'.
  3. Proportional Energy: The amount of energy (E) in each quantum is directly proportional to the frequency (ν) of the radiation. High-frequency light (like UV rays) has high-energy photons, while low-frequency light (like red light) has low-energy photons.

The Famous Equation

Planck gave the famous mathematical formula for the energy of a quantum:

E = hν

Where:

  • E = Energy of the quantum.
  • ν (nu) = Frequency of the radiation.
  • h = Planck's Constant (Its value is $6.626 \times 10^{-34}$ J·s).

Questions and Answers

What is Planck's quantum theory?+

Planck's quantum theory states that radiant energy is emitted or absorbed not continuously, but in small, discrete packets called 'quanta' or 'photons'. The energy of each quantum is directly proportional to its frequency (E=hν).

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