alleryStart learning →A 500-W room heater runs on 120-V AC power. What peak current does it draw?
A4.17 A
B2.95 A
C8.33 A
D5.89 A
Answer & Solution
Correct answer: D. 5.89 A
1. For AC, the quoted 500 W and 120 V are the average power and the rms voltage.
2. First find the rms current from P = IV: I = 500 W / 120 V.
3. Divide: I = 4.17 A rms.
4. The peak current is the rms current times the square root of 2, about 1.414.
5. Multiply: 4.17 A x 1.414 = 5.89 A.
6. 4.17 A is only the rms value, the trap of stopping one step early.
7. 2.95 A comes from dividing the rms current by 1.414 instead of multiplying, and 8.33 A doubles the rms current as if peak meant twice the average.
_Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.5 Alternating Current versus Direct Current_
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