(2 The electrons are accelerated by 4 The detector can be moved to detect A heated filament emits electrons. scattered electrons electrodes and directed at a crystal. at any angle u. b u Voltage source Electron beam (in vacuum) 3 Electrons strike a nickel crystal. Vba V - Va Vba 7 0, so electrons speed up in moving from a to b.

Question 2. (a) A beam of electrons is accelerated by a voltage of 180 V in a Davisson-Germer experi- ment. The electron beam is incident on the surface of a monocrystalline cobalt crystal oriented at 90° to the beam direction. A second-order beam is observed at 43.5°. What is the interatomic spacing of atoms in the cobalt crystal lattice? (b) The early experiments of Davisson & Germer used a polycrystalline nickel crystal. Ex- plain why they did not observe evidence for electron diffraction in their initial experi- ments. (c) i. A thermal neutron has an energy of E= 0.025 eV and a mass of 1.675 x 107 kg. Calculate the de Broglie wavelength of a thermal neutron. ii. On the basis of this result, explain whether it is possible to observe diffraction effects when the neutron is scattered by a cobalt crystal. Suggest a reason why performing neutron diffraction experiments is challenging.

To resolve an object in an electron microscope, the wavelength of the electrons must be close to the diameter of the object. What kinetic energy must the electrons have in order to resolve a protein molecule that is 7.00 nm in diameter? Take the mass of an electron to be kg.

What minimum accelerating voltage would be required to produce an x-ray with a wavelength of 0.0260 nm? V = kV