Classical · Module 08
Optics is where classical physics is at its most complete and also where it first fails. The double slit is the hinge between this module and everything quantum.
By the end of this module
You can explain colour, rainbows, cameras and the experiment that refuses to be classical.
Why does light bend when it enters glass?
Caltech
Fermat's principle. Light takes the fastest path, not the shortest — and that explains refraction in one line.
How can adding light to light produce darkness?
What does a photon 'know' about the angle of a filter?
What happens if I send the particles through one at a time?
Caltech
Feynman calls this the only mystery. Read it before starting quantum mechanics.
Check yourself
Every answer comes with the reasoning, not just a verdict. Getting one wrong and reading why is the point.
01Fermat's principle says light takes the path of least:
02In a double-slit experiment with electrons fired one at a time, the interference pattern:
03Placing a detector at one slit destroys the interference pattern because: