ITPEC FE Morning October 2021 Question 22
ITPEC FE Morning October 2021 — Question 22 of 80
Electrical Energy Calculation — compute watt-hours from a timing diagram.
Given: V = 100V, I = 10A, power factor = 1
Step 1 — Power:
- P = V × I × PF = 100 × 10 × 1 = 1000 W
Step 2 — Operating time from diagram:
- 0–60 min: Operating (60 min)
- 60–90 min: Stopped (0 min)
- 90–120 min: Operating (30 min)
- Total = 90 min = 1.5 hours
Step 3 — Energy:
- E = P × t = 1000 × 1.5 = 1,500 Wh
Why not others:
- (a) 1,000 — assumes only 60 min of operation
- (b) 1,200 — does not match any interval combination from the diagram
- (d) 2,000 — assumes full 120 min operation, ignoring the stopped period
Key rule: Energy (Wh) = Power (W) × Time (hours). Read timing diagrams carefully to sum only operating intervals.
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