Power Dissipated By Resistor is LRC Circuit

AI Thread Summary
The discussion revolves around calculating the average power dissipated by a 25-Ω resistor in an LRC series AC circuit with a power factor of 0.25 and a maximum voltage of 8.0 V. The initial calculation attempted to use the formula Pav = (1/2)(V)(I)cos(phi), but the user mistakenly substituted I incorrectly, leading to an incorrect power value of 0.32 W instead of the correct 0.08 W. Clarifications emphasize the importance of using Vrms rather than maximum voltage for accurate calculations in AC circuits. The conversation highlights the need to apply Ohm's Law correctly in the context of AC circuits. Understanding these principles is essential for accurate power dissipation calculations in electrical engineering.
mj23
Messages
2
Reaction score
0
[Note by mentor: this post does not use the homework template because it was originally posted in a non-homework forum.]

---------------------------------------------

Problem:
What is the average power dissipated by a 25-Ω resistor in an LRC series ac circuit for which the power factor is equal to 0.25 and the maximum voltage of the ac source is 8.0 V?

Answer: .08W

Attempt at Solution:
We know that Pav = (1/2)(V)(I)cos(phi) where cos(phi) is the power factor. So if we substitute I for V/I (ohms law) we get Pav = (1.2)((V^2)/R)cos(phi). Plugging in all the values I get that Pav = .32W which is clearly incorrect...

What did I do wrong?
Thanks for the advice!
 
Last edited by a moderator:
Physics news on Phys.org
mj23 said:
[Note by mentor: this post does not use the homework template because it was originally posted in a non-homework forum.]

---------------------------------------------

Problem:
What is the average power dissipated by a 25-Ω resistor in an LRC series ac circuit for which the power factor is equal to 0.25 and the maximum voltage of the ac source is 8.0 V?

Answer: .08W

Attempt at Solution:
We know that Pav = (1/2)(V)(I)cos(phi) where cos(phi) is the power factor. So if we substitute I for V/I (ohms law) we get Pav = (1.2)((V^2)/R)cos(phi). Plugging in all the values I get that Pav = .32W which is clearly incorrect...

What did I do wrong?
Thanks for the advice!
Check your formulas. What is Ohm's Law for an AC circuit? How do you get the average power in terms of Vrms and R?
 
ok i understand i made a typo by saying substitute I in for V/I meant V/R as you can see in the next step, but why do we need to use the Vrms in this situation rather than V?
 
mj23 said:
ok i understand i made a typo by saying substitute I in for V/I meant V/R as you can see in the next step, but why do we need to use the Vrms in this situation rather than V?
Well, you can use the maximum voltage and current if you like, but I=V/R is valid for the voltage across the resistor which is not the same as the given 8.0 V.
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Graphing the Power dissipated in a resistor
Replies
1
Views
2K
Power dissipated in this circuit with 2 batteries and 3 resistors
Replies
22
Views
4K
What is the role of cosφ in calculating power in LRC series circuits?
Replies
2
Views
2K
Circuit analysis: Six resistors and two batteries
Replies
1
Views
2K
Calculation of current in driven series RLC circuit
Replies
8
Views
2K
Power Resistor Immersed In Water
Replies
4
Views
3K
How Does Power Dissipation in One Resistor Relate to Total Power from Batteries?
Replies
1
Views
1K
Joule heating effect - qualitative explanation
Replies
8
Views
2K
What Power Is Dissipated by the R2 Resistor?
Replies
5
Views
7K
RC Circuit - Rate energy is dissipated in the resistor
Replies
4
Views
2K

Hot Threads

Recent Insights

Back
Top