An X-ray scattering from a free electron is observed to change its wavelength by 3.36 pmpm . Part A At what angle to the incident direction does the scattered X-ray move

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

Dshould be the right answer i think