A metal wire has a resistance per unit length of $0.92\,\Omega\,\text{m}^{-1}$. Its cross-sectional area is uniform and equal to $5.3 \times 10^{-7}\,\text{m}^2$. Calculate the resistivity of the metal in the wire.
A battery with electromotive force (e.m.f.) $E$ and negligible internal resistance is linked in series with a fixed resistor and a light-dependent resistor (LDR), as shown in Fig. 6.1. The fixed resistor has resistance $1400\,\Omega$. Because of the light shining on the LDR, its resistance is $1600\,\Omega$. A voltmeter across the LDR shows $6.4\,\text{V}$. Show that the current in the LDR is $4.0 \times 10^{-3}\,\text{A}$.
Calculate the number of free electrons passing through the LDR in a time of $3.2$ minutes.
Calculate the e.m.f. $E$.
Determine the ratio $\dfrac{\text{power dissipated in LDR}}{\text{power dissipated in fixed resistor}}$.
The environmental conditions change causing a decrease in the resistance of the LDR in (b). The temperature of the environment does not change. State whether there is a decrease, increase or no change to the intensity of the light illuminating the LDR.
State whether there is a decrease, increase or no change to the current in the battery.
State whether there is a decrease, increase or no change to the reading of the voltmeter.