Wave nature of electrons and de Broglie wavelengthEdexcel International A Level Physics: Mind map

Exam questions on Wave nature of electrons and de Broglie wavelength

1. A physics technician is demonstrating an electron diffraction tube. Electrons from a heated filament are accelerated and directed at a very thin polycrystalline graphite film inside an evacuated glass tube. A fluorescent screen beyond the film shows a pattern of concentric bright rings.
   Explain why the ring pattern is evidence for the wave nature of electrons.2 marks
2. A teacher compares the behaviour of electrons with that of larger moving objects such as a tennis ball. She uses the de Broglie equation, with Planck constant h = 6.63 × 10⁻³⁴ J s and electron mass 9.11 × 10⁻³¹ kg, and considers an electron moving at 4.0 × 10⁶ m s⁻¹ in a vacuum.
   Calculate the de Broglie wavelength of the electron moving at 4.0 × 10⁶ m s⁻¹.2 marks
3. Electrons in a beam have a kinetic energy of 4.0 × 10⁻¹⁷ J. The beam is directed at a crystal in which the spacing between neighbouring layers of atoms is 0.21 nm. A student wants to know whether the electrons will be noticeably diffracted by the crystal.
   Calculate the speed of an electron with kinetic energy 4.0 × 10⁻¹⁷ J.3 marks