Dissipation, resistance, and power.

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SUMMARY

The discussion centers on calculating the equivalent resistance and power dissipation of a series string of 19 Christmas tree lights connected to a 120 V source, dissipating 60 W. The equivalent resistance of the light string is determined using the formula R = V²/P, resulting in 240 ohms. When one bulb burns out and shorts, reducing the total number of bulbs to 18, the new resistance is calculated, and the new power dissipation can be found using the same power formula. The discussion emphasizes the importance of understanding the relationship between voltage, current, and resistance in electrical circuits.

PREREQUISITES
  • Understanding of Ohm's Law (V = IR)
  • Familiarity with power dissipation formulas (P = IV, P = V²/R)
  • Basic knowledge of series circuits
  • Ability to manipulate algebraic equations
NEXT STEPS
  • Calculate the equivalent resistance of different series circuits
  • Explore the effects of bulb failure in series circuits
  • Learn about power dissipation in resistive loads
  • Investigate the impact of voltage changes on power and resistance
USEFUL FOR

Students studying electrical engineering, hobbyists working with series circuits, and anyone interested in understanding power dissipation in electrical systems.

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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