4-2 Quantum Theory

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# 4-2 Quantum Theory - PowerPoint PPT Presentation

4-2 Quantum Theory. Planck’s Theory. Max Planck predicted accurately how the spectrum of radiation emitted by an object changes with temperature. Proposed that there is a fundamental restriction on the amounts of energy that an object emits or absorbs, called quantum. Means FIXED AMOUNTS.

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### 4-2 Quantum Theory

Planck’s Theory
• Max Planck predicted accurately how the spectrum of radiation emitted by an object changes with temperature.
Proposed that there is a fundamental restriction on the amounts of energy that an object emits or absorbs, called quantum.
• Means FIXED AMOUNTS
Completely contradicted the idea that energy can emit or absorb in any amount.
• Related the Frequency of the radiation to the amount of energy.
• E = h
• Energy = Planck’s Constant x Frequency
• Energies absorbed or emitted by atoms are quantized, which means that their values are restricted to certain quantities. Energy is not continuous
Example
• Imagine a car’s fundamental quantum of energy corresponds to a speed of 10 km/hr. If the car has 7 quanta of energy, it will have a speed of 70 km/hr. If the car has 9 quanta of energy, it will have a speed of 90 km/hr. This shows that a car can only move in multiples of 10 km/hr (in this case). Speeds such as 88 km/hr and 41 km/hr are impossible
Why can’t we see quantized energy around us?
• Planck’s Constant is very small. The Quanta are too small for every day notice, but to a very small atom they make a big difference
The Photoelectric Effect
• In the photoelectric effect, electrons are ejected from the surface of a metal when light shines on it.
• Einstein realized that Planck’s idea of energy quanta could explain this.
• Said that Light consists of quanta of energy that behave like tiny particles, called PHOTONS
Red light will not cause electrons to flow in a sheet of sodium metal, no matter how long or bright the source is. Violet light will cause electrons to flow. Violet light has a greater frequency, and a greater amount of energy per photon
The frequency of light and the energy of the photon explains the effects of electromagnetic radiation.
• X-rays contain high amounts of energy because of their frequency, while radio waves have low frequency and low energy.