Question

If electrical energy costs 12 cents, or $0.12, per kilowatt-hour, then what would the following events cost? (a) Burn a 40 Wlight bulb for 24 h straight. (b) Operate an electric oven for 6.0 hif it carries a current of 20.0 A at 220 V.

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asked 2021-01-24
If electrical energy costs 12 cents, or $0.12, per kilowatt-hour, then what would the following events cost?
(a) Burn a 40 Wlight bulb for 24 h straight.
(b) Operate an electric oven for 6.0 hif it carries a current of 20.0 A at 220 V.

Answers (1)

2021-01-25
For part a)
We have $0.12 / kW hr @ 24 hours. The Cost formula is: \(\displaystyle\text{Cost}=\text{Power (P)}\times\text{Time used (Hr) }\ \times\text{Cost per kW/hr}\)
\(\displaystyle{P}={40}{W}\to{0.040}{k}{W}\)
Plug it all into the formula:
Cost = (0.040kW)(24hr)($0.12/kW hr)
Cost = 11.52 cents or $0.12 (when rounded)
For part b)
We have the following information:
$0.12 /kW hr @ 6.0hr
I=20.0A
V=220V
\(\displaystyle{I}={\frac{{{P}}}{{{V}}}}\to{P}={\left({V}\right)}{\left({I}\right)}\)
P = (220V)(20.0A)
\(\displaystyle{P}={4400}{W}\to{4.4}{k}{W}\)
Now use the Cost formula from above in part a.
\(\displaystyle\text{Cost}=\text{Power (P)}\times\text{Time used (Hr) }\ \times\text{Cost per kW/hr}\)
Cost = (4.4kW)(6.0hr)($0.12/kW hr)
Cost = 316.8 cents = $3.17 when rounded.
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