A battery with an electromotive force (e.m.f.) $12\,\text{V}$ and negligible internal resistance is joined to a fixed resistor of resistance $40\,\Omega$ and a thermistor of resistance $R_T$, as illustrated. At first, the thermistor is at a temperature of $15^{\circ}\text{C}$, and the current in the circuit is $0.10\,\text{A}$. The thermistor is then heated or cooled, causing the current to rise to $0.12\,\text{A}$. State how the temperature of the thermistor changes and determine $R_T$ at the new temperature.
- Atemperature increases, $R_T = 60\,\Omega$
- Btemperature decreases, $R_T = 60\,\Omega$
- Ctemperature increases, $R_T = 100\,\Omega$
- Dtemperature decreases, $R_T = 100\,\Omega$