E.2.8 (HL)—Photon wavelength increase

Follow the energy transfer

After Compton scattering, the photon has transferred energy to the electron. Its final energy is lower than its initial energy.

Convert energy to wavelength

Since $E=hc/\lambda$, lower photon energy means larger wavelength. Therefore the scattered photon has a longer wavelength than the incident photon.

Keep the direction of change

The wavelength shift is zero only for no energy transfer. A stronger transfer to the electron produces a larger positive $\Delta\lambda$, subject to the scattering geometry.

Common trap

Do not infer a shorter wavelength from a lower photon energy. Energy and wavelength are inversely related.