Q1/The power supplied to a typical black-and-white television set is 90 W when t
ID: 1316021 • Letter: Q
Question
Q1/The power supplied to a typical black-and-white television set is 90 W when the set is connected to 120 V.
(a) How much electrical energy does this set consume in 1 hour?
J
(b) A color television set draws about 2.1 A when connected to 120 V. How much time is required for it to consume the same energy as the black-and-white model consumes in 1 hour?
min
Q2/The cost of electricity varies widely throughout the United States; $0.120/kWh is a typical value. At this unit price, calculate the cost that would result from each of the following.
(a) Leaving a 40.0 W porch light on for 2 weeks while you are on vacation.
$
(b) Making a piece of dark toast in 3.00 min with a 980 W toaster.
$
(c) Drying a load of clothes in 40.0 min in a 4900 W dryer.
$
Explanation / Answer
1.
a)
Energy
E=P*t=90*(1*60*60)
E=324,000 J or 3.24*105 J
b)
Power consumed by color set
P=VI=120*2.1=252 Watts
time
t=E/P= 3.24*105/252
t=21.43 min
2.
a)
Energy
E=P*t=40*(2*7*24)
E=13440 W=13.44 KWH
Cost
C=13.44*0.12 =$1.613
b)
Energy
E=(3/60)*(980/1000)
E=0.049 KWH
Cost
C=0.049*0.12=$0.00588
c)
E=(40/60)(4900/1000)
E=3.26 KWH
Cost
C=$0.12*3.26
C=$0.392
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