🔍 Key Concepts

• Carefully identify which resistor is the series resistor in diagram B when the switch is closed • Find the equivalent resistance of R1 and R2 in the parallel branch, then add the series resistor • Use power formulas: P = I^2 R and P = V × I

💭 Think About

• In diagram B, which resistor has the same current as the source, and which resistors share the current? The one with the same current is the series resistor. • Once you replace the parallel pair with a single equivalent resistance, what is the total circuit resistance, and therefore the circuit current from a 30‑volt source? • After you find the current, how can you use it with the resistance of the series resistor alone to get the power it consumes?

✅ Before You Answer

• Be sure you combined R1 and R2 as parallel resistors: ( R_{eq} = \frac{R_1 R_2}{R_1 + R_2} ) • Confirm that the total resistance is series sum: ( R_T = R_3 + R_{eq} ) • Check that you used the current through the series resistor only when applying ( P = I^2 R ) or ( P = V I )