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Concept · Modern Physics
Relativity & duality (foundational)
two postulates of special relativity, time dilation / length contraction (qualitative), wave-particle duality and de Broglie matter waves
Switches you to Physics
Named traps
9 ways this goes wrong.
Each is a named misconception the questions are built to catch. Open one for the move that tempts, and the fix.
- Length contraction misdirectedContracts a moving object's dimension perpendicular to its motion, or expands it, instead of shortening only the length along the direction of motion.→
- Light speed frame-dependentAdds the source or observer velocity to the speed of light, violating the postulate that c is the same in all inertial frames.→
- Massless photon has no momentumConcludes a photon has zero momentum because it is massless, ignoring p=h/λ.→
- Only light has wave natureBelieves wave behavior applies only to light, not to electrons or other particles.→
- Photon has rest massAssigns a nonzero rest mass to the photon.→
- Time dilation reversedConcludes a fast-moving clock runs faster (rather than slower) as seen by a stationary observer.→
- Wave and particle seen at onceThinks a single experiment shows both wave and particle behavior simultaneously, ignoring complementarity.→
- de Broglie ignores speed/massComputes de Broglie wavelength without using the particle's momentum (mass times velocity).→
- de Broglie proportional to momentumTreats de Broglie wavelength as proportional to momentum rather than λ=h/p (inverse).→
Key formulas
No formula sheet is matched to this concept yet. Work it from first principles, and watch the traps.
Shaky underneath?
If the concept underneath still feels loose, patch it here before coming back to CSCA questions.
FoundationsPhysics 2 breadthMechanics foundations