1. Problem 1: Determine the resistance when current $I=0.8$ A and voltage $V=20$ V. Using Ohm's law: $$R = \frac{V}{I} = \frac{20}{0.8} = 25\,\Omega$$ 2. Problem 3: An electric kettle has resistance $R=30\,\Omega$, voltage $V=240$ V. Find (a) the current $I$ and (b) power rating $P$. (a) Current using Ohm's law: $$I = \frac{V}{R} = \frac{240}{30} = 8\, A$$ (b) Power rating using power formula: $$P = I^{2} \times R = 8^{2} \times 30 = 64 \times 30 = 1920\, W = 1.92\, kW$$ 3. Problem 4: Electric motor winding with current $I=5$ A and resistance $R=100\,\Omega$. Find (a) p.d. $V$ across winding and (b) power dissipated $P$. (a) Voltage across winding: $$V = I \times R = 5 \times 100 = 500\, V$$ (b) Power dissipated: $$P = I^{2} \times R = 5^{2} \times 100 = 25 \times 100 = 2500\, W$$ 4. Problem 5: Resistance of coil with current drawn from $V=120$ V supply: (a) For current $I = 50$ mA $= 50 \times 10^{-3} = 0.05$ A, $$R = \frac{V}{I} = \frac{120}{0.05} = 2400\,\Omega$$ (b) For current $I = 200\, \mu A = 200 \times 10^{-6} = 0.0002$ A, $$R = \frac{V}{I} = \frac{120}{0.0002} = 600000\,\Omega = 600\, k\Omega$$ 5. Problem 5 (additional): Hot resistance of filament lamp $R=960\,\Omega$, voltage $V=240$ V. Current taken: $$I = \frac{V}{R} = \frac{240}{960} = 0.25\, A$$ Power rating: $$P = I^{2} \times R = 0.25^{2} \times 960 = 0.0625 \times 960 = 60\, W$$