The cost of energy delivered to residences by electrical transmission varies from $0.070/kWh to $0.258/kWh throughout the United States; $0.110/kWh is the average value. At this average price, calculate the cost of:. (a) leaving a 40.0-W porch light on for two weeks while you are on vacation,
(b) making a piece of dark toast in 3.00 min with a 970-W toaster, and
(c) drying a load of clothes in 40.0 min in a 5.20 3 103-W dryer

(a) $ 1.48

(b) $ 0.005

(c) $ 0.38

Explanation:

(a)

First, we calculate the energy consumed, by using following formula:

E = Pt

where,

E = Energy Consumed = ?

P = Power Delivered = (40 W)(1 KW/1000 W) = 0.04 KW

t = Time Duration = (2 weeks)(7 days/week)(24 h/day) = 336 h

Therefore,  

E = (0.04 KW)(336 h) = 13.44 KWh

Now, we calculate cost, by following formula:

Cost = (E)(Unit Price)

Cost = (13.44 KWh)($ 0.11/KWh)

Cost = $ 1.48

(b)

First, we calculate the energy consumed, by using following formula:

E = Pt

where,

E = Energy Consumed = ?

P = Power Delivered = (970 W)(1 KW/1000 W) = 0.97 KW

t = Time Duration = (3 min)(1 h/60 min) = 0.05 h

Therefore,  

E = (0.97 KW)(0.05 h) = 0.0485 KWh

Now, we calculate cost, by following formula:

Cost = (E)(Unit Price)

Cost = (0.0485 KWh)($ 0.11/KWh)

Cost = $ 0.005

(c)

First, we calculate the energy consumed, by using following formula:

E = Pt

where,

E = Energy Consumed = ?

P = Power Delivered = (5.203 x 10³ W)(1 KW/1000 W) = 5.203 KW

t = Time Duration = (40 min)(1 h/60 min) = 0.67 h

Therefore,  

E = (5.203 KW)(0.67 h) = 3.47 KWh

Now, we calculate cost, by following formula:

Cost = (E)(Unit Price)

Cost = (3.47 KWh)($ 0.11/KWh)

Cost = $ 0.38

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