(a) An X-ray photon scatters from a free electron at an angle u from its initial direction of motion. As the scattering angle u increases, does the change in wavelength Δ ( of the photon increase, decrease, or remain the same?

(b) Choose the best explanation from among the following:

I. A larger scattering angle means a larger transfer of momentum and thus a larger change in wavelength of the photon.

II. A larger scattering angle means a larger change in frequency and thus a smaller change in wavelength.

III. Photons always scatter elastically, so that the energy of the scattered photon does not change and neither does its wavelength?