Physics 9702 · AS & A Level · Energy and momentum of a photon
Energy and momentum of a photon — practice question
A photon with wavelength $6.50 \times 10^{-12}\,\text{m}$ strikes an isolated electron that is initially at rest, as shown in Fig. 8.1. The electron of mass $m_e$ scatters the photon elastically. After deflection, the photon has wavelength $6.84 \times 10^{-12}\,\text{m}$.
(a(i))[2]
Calculate the momentum of the incident photon.
(a(ii))[2]
Calculate the energy of the incident photon.
(b(i))[2]
The deflection angle $\theta$ is related by the expression $\Delta \lambda = \frac{h}{m_e c}(1 - \cos \theta)$, where $\Delta \lambda$ denotes the change in the photon wavelength, $h$ is the Planck constant and $c$ is the speed of light in free space. Calculate the angle $\theta$.
(b(ii))[3]
Use energy arguments to suggest why $\Delta \lambda$ must always be positive.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$p=h/\lambda$” …