Calculate the number of protons that would have a charge of one coulomb. (Proton charge $=+1.6\times {10}^{-19}\mathrm{C}$.)

A length of copper wire is joined in series to a length of silver wire of the same diameter. Both wires have a current in them when connected to a battery. Explain how the mean drift velocity of the electrons will change as they travel from the copper into the silver. Electron number densities:

Copper $\mathrm{n}=8.5\times {10}^{28}{ \mathrm{m}}^{-3}$

Silver $\mathrm{n}=5.9\times {10}^{28}{ \mathrm{m}}^{-3}$.

You can buy lamps of different brightness to fit in light fittings at home (Figure). A $100$ watt lamp glows more brightly than a $60$ watt lamp. Explain which of the lamps has the higher resistance.

(a ) Calculate the potential difference across a motor carrying a current of $1.0 \mathrm{A}$ and having a resistance of $50\Omega$.