Q.In a photon-electron collision ______

The Compton effect (or Compton scattering), discovered by Arthur Compton in 1923-24, provided the first direct experimental proof that a photon carries momentum as well as energy -- confirming the full particle character of electromagnetic radiation beyond what the photoelectric effect alone had shown. In the experiment, a monochromatic beam of X-rays of wavelength $\lambda$ was scattered off a graphite target, and the scattered radiation was found to contain intensity peaks at TWO wavelengths: the original wavelength $\lambda$, and a slightly longer wavelength $\lambda'=\lambda+\Delta\lambda$, where the shift $\Delta\lambda=\frac{h}{m_ec}(1-\cos\theta)$ depends only on the scattering angle $\theta$, never on the incident wavelength itself. …