They added this new chapter into SPM Physics which is very good. Quantum Physics called modern physics compared with the Newtonian physics they have in the syllabus for a long time. Here are the notes for this new Topic.
Quantum Theory of Light
- Light has long been explained as Wave.
- But after many experiments, modern scientist finds out that Light can be explained as small particles of energy.
- Small particles of energy are called Quantum.
- Quantum of energy is discrete energy packet.
- Photon is a packet of quantum of energy.
- This is how it looks like. (Visual 1)
- Therefore different colour lights has different energy (the unit is in eV and not Joules,J) (Visual 2)
- This is how it visually looks like for different colours (Visual 3)
3 Formulas you need to learn
- Energy in photons (photons = light in particles form)
- Different light has different wavelength, for example red light is 650 nm and blue light is 450 nm.
- Therefore using the formula E = hf, you can find the energy in the photons (light)
This formula is to relate Energy with Frequency of light. (Visual 4)
This formula is to relate Energy with the Wavelength of light. (Visual 5)
This formula is to relate the Power with the Frequency of light. (Visual 6)
Since ‘n’ is the number of photos, the more photons we have in one second the higher the power of the light.
Wave – Particle Duality
- Light is even more useful if we can explain in terms of both wave and in terms of particles.
- De Broglie manage to explain light as both wave and particle (quantum).
- Here’s the formula he derived, which can relate wavelength and momentum. (Visual 7)
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