Paper 2 Current Electricity Fundamentals Answers

Q1 Charge flow and power

1. $t=240\mathrm{s}$, $Q=It=3.50(240)=840\mathrm{C}$. [2]
2. $E=VIt=12.0(3.50)(240)=1.01\times 10^4\mathrm{J}$. [2]
3. $R=V/I=12.0/3.50=3.43\Omega$. [2]

Q2 Resistivity

1. $\rho =RA/L=4.6(2.5\times 10^{-7})/1.80=6.39\times 10^{-7}\Omega \mathrm{m}$. [3]
2. Resistance doubles. [1]
3. Resistivity depends on material and temperature, not on the object’s length or cross-sectional area. [2]

Q3 Internal resistance

1. Lost volts $=Ir=0.80(0.35)=0.28\mathrm{V}$. [2]
2. $V=\mathcal{E}-Ir=1.60-0.28=1.32\mathrm{V}$. [2]
3. Some energy per unit charge is dissipated inside the cell due to internal resistance, so less energy per unit charge is delivered to the external circuit. [2]