Key Concepts: Use $V = IR$ to relate voltage, current, and resistance.
Section A: Calculations
1. A resistor has $V = 9\,V$ and $I = 3\,A$. Calculate $R$. [2]
2. A resistor has $R = 8\,\Omega$ and $I = 0.5\,A$. Calculate $V$. [2]
3. A bulb has $V = 12\,V$ and $R = 6\,\Omega$. Calculate $I$. [2]
Section B: Reasoning
4. Explain what happens to current if resistance increases and voltage is constant. [2]
5. A resistor of $5\,\Omega$ carries a current of $2\,A$. Calculate the voltage. [2]
6. A $4\,\Omega$ resistor is connected to a 12 V supply. Calculate the current. [2]
7. A heater takes 3.0 A from a 230 V supply. Calculate the resistance and power. [3]
Total marks: 15
Mark Scheme
1. $R = V/I = 9/3 = 3\,\Omega$ [2]
2. $V = IR = 0.5 \times 8 = 4\,V$ [2]
3. $I = V/R = 12/6 = 2\,A$ [2]
4. Current decreases [2]
5. $V = IR = 2 \times 5 = 10\,V$ [2]
6. $I = V/R = 12/4 = 3\,A$ [2]
7. $R = V/I = 230/3.0 \approx 77\,\Omega$; $P = VI = 230 \times 3.0 = 690\,W$ [3]