Question

A 500 watt heating unit is designed to operate from a 115 Volt line. If the line voltage drops to 110 volt, the percentage drop in heat output will be

• A. 10.20%
• B. 8.1%
• C. 8.6%
• D. 7.6%

Answer 1

Answer: (C)

8.6%

Answer 2

By using $P_{consumed} = \left( \frac{V_{A}}{V_{R}} \right)^{2} \times P_{R}$

⇒ $P_{Consumed} = \left( \frac{110}{115} \right)^{2} \times 500 = 456.6Watt$

So % drop in heat output

$= \frac{P_{Actual} - P_{Consumed}}{P_{Actual}} \times 100 = \frac{(500 - 456.6)}{500} \times 100 = 8.6\%$