Define potential difference (p.d.) in words.
A battery with electromotive force $20\,\text{V}$ and zero internal resistance is connected in series with two resistors $R_1$ and $R_2$, as shown in Fig. 6.1. The resistance of $R_2$ is $600\,\Omega$. The resistance of $R_1$ is changed from $0$ to $400\,\Omega$. Calculate (i) the maximum p.d. across $R_2$, (ii) the minimum p.d. across $R_2$.
Calculate the greatest p.d. across $R_2$.
Calculate the smallest p.d. across $R_2$.
A light-dependent resistor (LDR) is connected in parallel with $R_2$, as shown in Fig. 6.2. As the light intensity is changed, the resistance of the LDR varies from $5.0\,\text{k}\Omega$ to $1.2\,\text{k}\Omega$. For the maximum light intensity, calculate the total resistance of $R_2$ and the LDR.
The resistance of $R_1$ is changed from $0$ to $400\,\Omega$ in the circuits of Fig. 6.1 and Fig. 6.2. State and explain any difference between the minimum p.d. across $R_2$ in each circuit. You do not need to give numerical values.