In the below circuit diagram, calculate:
the current I2.
Topic: Current, resistance and circuits
Answer
The 12 Ω and 8 Ω are in parallel, so the SAME voltage appears across both.
Voltage across the parallel section, using the 12 Ω branch (I₁ = 0.4 A): V_p = I₁ × 12 = 0.4 × 12 = 4.8 V
Current through the 8 Ω branch: I₂ = V_p ÷ 8 = 4.8 ÷ 8 = 0.6 A
Current I₂ = 0.6 A
Parallel means equal VOLTAGE, not equal current. So find the voltage from the branch you know about, then use it on the branch you do not.
The smaller resistance carries the larger current — 0.6 A through the 8 Ω against 0.4 A through the 12 Ω. Current takes the easier path. If your answer had the 8 Ω carrying less current than the 12 Ω, you have the division upside down.
A quicker route for two parallel branches: the currents are in the inverse ratio of the resistances, so I₁ : I₂ = 8 : 12 = 2 : 3, and 0.4 × 3/2 = 0.6 A.