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4 votes
A lamp uses 28.5 amps of current and has a resistance of 12.8 ohms. How much power does it use?

A.365 watts
B.4670 watts
C.63.5 watts
D.10,400 watts

User Maxxxo
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6.7k points

2 Answers

4 votes
One of the formulas for electrical power is

Power = (current²) x (resistance) .

This is a very handy formula to use right now. because this question TELLS us the current and the resistance, and it wants us to find the power. Let's go:

Power = (current²) x (resistance) .

= (28.5 A)² x (12.8 ohms)

= 10,396.8 watts .

Choice-D is apparently the one to pick.


This is a serious lamp ... one you don't want to mess with.
A typical incandescent lamp is maybe 20% efficient ...
20% of the power it uses gets turned into light, and the
other 80% gets turned into heat. If that's true of the lamp
in this question, then when it's turned on ...

-- it shines with about 2,080 watts of light;

-- it oozes about 8,320 watts of heat into the room ... about
the same as five or six toasters, or seven blow-dryers, all
running full-blast.

User Mstrand
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7.2k points
5 votes
D. 10,400
Power=1^2*R = 28.5*28.5*12.8 = 10396.8 W
User Barny
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7.1k points