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Question:

Calculate the power used in the 2Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1Ω and 2Ω resistors, and (ii) a 4 V battery in parallel with 12Ω and 2Ω resistors.

Solution:

Step 1 - Calculation of power in 1st circuit : P=V²/Req. Req.=1Ω+2Ω=3Ω ∴P=(6V)²/3Ω=12 watt
Step 2 - Calculation of Power in 2nd circuit : P=V²/Req. Req.=2Ω×12Ω/2Ω+12Ω=24/14=12/7Ω
P=(4V)²/(12/7)Ω=9.33 watt.