This preview shows pages 1–2. Sign up to view the full content.
Jim Guinn’s PHYS2212 Assignment #10 Solutions
1.
A 10
4
Ω
carbon resistor used in electronic circuits is rated at 0.25W .
a)
What maximum current can this resistor carry?
The maximum current is I = (P / R)
1/2
=
5mA .
b)
What maximum voltage can be placed across this resistor?
The maximum voltage is V = (P R)
1/2
=
50V .
2.
If energy costs 9 cents per kilowatthour,
1 kWhr = (1x10
3
J/s) (3600s) = 3.6x10
6
J .
a)
How much does it cost to operate an electric toaster for 4 min if the toaster has
resistance 11.0
Ω
and is connected across 120V?
The power dissipated in the toaster is P = V
2
/ R = 1.31kW .
Operating for 4min (1/15 hr)
gives a cost of (1.31kW) (1/15 hr) (9 cents / kWhr) =
0.79 cents.
b)
How much does it cost to operate a heater of resistance 5.0
Ω
connected across 120V
for 8hours?
In this case, P = 2.88kW , therefore the cost is
$2.07 .
3.
a)
Find the equivalent resistance between points “a” and “b”.
The two resistors in parallel give an equivalent resisance of [(1 / (6
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 Fall '11
 JimGuinn

Click to edit the document details