Energy from voltage and resistance: A 15 V source is applied across a 12 Ω resistor. How much electrical energy is used in three minutes (expressed in watt-hours)?

Introduction / Context:
Translating circuit parameters to energy consumed over a time interval is vital for estimating battery life and energy costs. With voltage and resistance known, you can compute power and then energy by accounting for time.

Given Data / Assumptions:

• Voltage V = 15 V.
• Resistance R = 12 Ω.
• Time t = 3 minutes = 0.05 h = 180 s.
• Purely resistive load; steady operation.

Concept / Approach:

Compute power first: P = V^2 / R. Then compute energy: E = P * t. Keep units consistent; since answers are in Wh, express time in hours.

Step-by-Step Solution:

Verification / Alternative check:

In joules: E = P * t = 18.75 W * 180 s = 3,375 J. Convert to Wh: 3,375 J / 3600 ≈ 0.9375 Wh. Both paths agree.

Why Other Options Are Wrong:

56.25 Wh would require one hour at 56.25 W, not 0.05 h at 18.75 W. 5.6 Wh and 938 Wh are off by large factors. 0.0938 Wh is 10× too small.

Common Pitfalls:

Forgetting to convert minutes to hours when answers are in Wh; using P = V * I without computing I correctly; arithmetic slips with squares.

Final Answer:

0.938 Wh