Dissipation, resistance, and power.

AI Thread Summary
The discussion revolves around calculating the equivalent resistance of a series of 19 Christmas tree lights connected to a 120 V source that dissipates 60 W. The equivalent resistance of the light string can be determined using the power and voltage formulas. When one bulb burns out and shorts, the resistance of the string changes, necessitating a recalculation of both the new resistance and the power dissipation. Participants suggest using the known power and voltage to find the resistance and then adjusting for the change when a bulb fails. The conversation emphasizes applying formulas for power and resistance to solve the problem effectively.
exohemmx3
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Homework Statement


A string of 19 identical Christmas tree lights
are connected in series to a 120 V source. The
string dissipates 60 W.
What is the equivalent resistance of the
light string? Answer in units of ohms.
What is the resistance of a single light? An-
swer in units of .

What power is dissipated in a single light?
Answer in units of W.

One of the bulbs burns out. The lamp has a
wire that shorts out the bulb filament when it
burns out, dropping the resistance of the bulb
to zero.
What is the resistance Rnew of the light
string now? Answer in units of ohms.

Find the power Pnew dissipated by the string
now. Answer in units of W.



Homework Equations


P=IV
I=V/R
P=(V/R)V
R=V2/R


The Attempt at a Solution


I'm not sure how to start, since the dissipation of power is in watts. thanks for any hints or help you can give !
 
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exohemmx3 said:
I'm not sure how to start, since the dissipation of power is in watts. thanks for any hints or help you can give !

Welcome to PF.

Well you have Power dissipated, and you have the Voltage don't you?

Can't you figure the resistance of the 19 bulbs together?

And if then the 19 become 18 what happens if figure power again from the same formula?
 
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