(a)[4]
Use band theory to explain why the resistance of the copper wire rises as its temperature rises.
(b)[4]
The copper crystal structure is to be examined using electron diffraction. Electrons, after being accelerated from rest through a potential difference $V$, are directed onto the crystal. The de Broglie wavelength $\lambda$ of the electrons is $2.6 \times 10^{-11}\,\text{m}$. Calculate the accelerating potential difference $V$.