X-rays scatter from a graphite target and show a shift in wavelength that depends on scattering angle. Classical wave theory cannot explain a wavelength change from scattering off free electrons. Which statement best explains what this indicates about electromagnetic radiation?
- Radiation behaves as photons with momentum that can be transferred in collisions. (correct answer)
- Radiation is only a wave, and the wavelength shift is caused by diffraction alone.
- Radiation becomes particle-like only when a human observes the scattered X-rays.
- Radiation consists of charged waves that lose charge and lengthen in wavelength.
Explanation: This question tests understanding of quantum theory and wave-particle duality. Compton scattering demonstrates that electromagnetic radiation behaves as particles (photons) with momentum p = E/c = h/λ, where collisions with electrons follow conservation of energy and momentum like billiard balls. The wavelength shift occurs because photons transfer some energy and momentum to electrons, resulting in lower-energy (longer-wavelength) scattered photons. Choice B reflects the classical wave misconception that electromagnetic radiation is purely wavelike and cannot explain momentum transfer in particle-like collisions. When analyzing high-energy radiation interactions, recognize that photons carry both energy and momentum as discrete quanta, not as continuous waves.