02-08 Watt's Law & Ohm's Law Exercises

Let's test our understanding of Ohm's Law and Watt's Law.

Q1: The switch is turned on, or closed. What are the voltages at A, B, C and D?

A: 0V by convention. Other answers may apply.
B: +10V
C: +10V. Wires are assumed to have zero resistance.
D: 0V. Wires are assumed to have zero resistance.

Q2: How does the answer to Q1 change, if the switch is open?

A: 0V by convention.
B: +10V
C: 0V.
D: 0V.

Q3: The bulb is rated at 10W power. What is the current I that flows through the circuit?

P = V * I
10W = 10V * I
→ I = 1A

Q4: How much will it cost you per month to run the bulb 24 hours a day? Assume the old TNB rate of RM 0.218/kWh.

Energy consumed = Power * Time
Energy consumed = 10W * 24h/day * 30days/month
Energy consumed = 7200 Wh/month
Energy consumed = 7.2 kWh/month

Cost to run = 7.2 kWh/month * RM 0.218/kWh
Cost to run = RM 1.57/month

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