State Kirchhoff’s first law in words.
In Fig. 5.1, the circuit includes a battery with electromotive force (e.m.f.) $E$ and negligible internal resistance, connected to four resistors $R_1$, $R_2$, $R_3$ and $R_4$, each with resistance $R$. The current in $R_3$ is $0.30\,\text{A}$, while the potential difference (p.d.) across $R_4$ is $2.4\,\text{V}$.
Show that the value of $R$ is $4.0\,\Omega$.
Determine the battery e.m.f. $E$.
The battery in (b) is changed to another battery with the same e.m.f. $E$, but with internal resistance that is not negligible. State and explain whether the total power produced by the battery changes, and if so how.
The resistors in Fig. 5.1 are constructed from nichrome wire of uniform radius $240\,\mu\text{m}$. Each resistor requires a wire length of $0.67\,\text{m}$. Calculate the resistivity of nichrome.