MYP Physics sample question: Current, voltage and resistance in parallel circuits

A 6 Ω resistor and a 12 Ω resistor are connected in parallel to a 12 V cell.

1. (a)Calculate the current in each resistor.[2]
   Show the mark scheme for (a)

   • • I = V ÷ R (1)
   • • 6 Ω: 2.0 A; 12 Ω: 1.0 A (1)
2. (b)State the total current drawn from the cell.[1]
   Show the mark scheme for (b)

   • • 2.0 + 1.0 = 3.0 A (1)
3. (c)Calculate the total resistance of the circuit.[2]
   Show the mark scheme for (c)

   • • R = V ÷ I = 12 ÷ 3.0 (1)
   • • R = 4.0 Ω (1)
4. (d)Give one reason why household lights are wired in parallel.[1]
   Show the mark scheme for (d)

   • • Each lamp receives the full supply voltage and can be switched on and off independently (1)

In parallel, the voltage across each branch is the same and the currents add. The total resistance is always smaller than the smallest branch.