Question

10 W is to be delivered to a device via a wire having resistance \(2\,\Omega\). If 20 V is the voltage across the device, the power wasted in the process is:

• A. 3 W
• B. 2 W
• C. 0.5 W
• D. 1.5 W

Hint:

Use \(P_{loss} = I^2R\) when current is known; use \(VI\) only when voltage drop is required.

Answer 1

The Correct Option is C

Step 1: Device current.
P = VI → 10 = 20 × I → I = 0.5 A.

Step 2: Voltage drop across wire.
V_loss = IR = 0.5 × 2 = 1 V.

Step 3: Power dissipated in wire.
P_loss = I²R = (0.5)² × 2.

Step 4: Numerical evaluation.
P_loss = 0.25 × 2 = 0.5 W.

Step 5: Physical origin.
This waste is Joule heating in the connecting leads.

Step 6: Conclusion.
The wasted power is 0.5 W.