State what is meant by the de Broglie wavelength of an electron.

 The diagram shows the principles of an electron tube used to demonstrate electron diffraction.

 Calculate the kinetic energy $E$ (in joules) of the electrons incident on the graphite film.

The diagram shows the principles of an electron tube used to demonstrate electron diffraction.

Show that the momentum of an electron is equal to $\sqrt{2 E m_{e}}$ where $m_{\mathrm{e}}$ is the mass of an electron, and hence calculate the momentum of an electron. $\left(m_{\mathrm{e}}=9.11 \times 10^{-31} \mathrm{~kg}\right)$

 The diagram shows the principles of an electron tube used to demonstrate electron diffraction.

Calculate the de Broglie wavelength of the electrons.

Light of wavelength $550 \mathrm{nm}$ is incident normally on a metal plate. The intensity of the light is $800 {\mathrm{Wm}}^{-2}$. All the incident light is absorbed by the metal plate. The plate has dimensions $5.0\mathrm{cm}\times 5.0\mathrm{cm}$.

Explain how the light hitting the plate exerts force on the plate.

(b) Light of wavelength $550 \mathrm{nm}$ is incident normally on a metal plate. The intensity of the light is $800 {\mathrm{Wm}}^{-2}$. All the incident light is absorbed by the metal plate. The plate has dimensions $5.0\mathrm{cm}\times 5.0\mathrm{cm}$. Calculate the momentum of each photon of light. (Use: $h=6.63\times {10}^{-34} \mathrm{J} \mathrm{s}$)

(b) Light of wavelength $550 \mathrm{nm}$ is incident normally on a metal plate. The intensity of the light is $800 {\mathrm{Wm}}^{-2}$. All the incident light is absorbed by the metal plate. The plate has dimensions $5.0\mathrm{cm}\times 5.0\mathrm{cm}$. Calculate the force exerted on the plate due to the light.