Circuit problem- resistance, power, voltage

AI Thread Summary
The discussion revolves around calculating the internal resistance and driving voltage of a battery connected to two different resistors, R1 = 2 Ω and R2 = 0.5 Ω, both consuming 2W of power. Initial calculations led to an internal resistance of 1/3 Ω and a voltage of 2.33 V, but after further review and adjustments, the final results were determined to be an internal resistance of 1 Ω and a driving voltage of 3 V. Participants confirmed the correctness of these calculations and expressed gratitude for the assistance received. The thread highlights the importance of careful equation manipulation and verification in solving circuit problems. Overall, the discussion effectively resolved the initial query regarding the circuit parameters.
mmoadi
Messages
149
Reaction score
0

Homework Statement



We connect two resistors to a battery, once with the resistor of the resistance R1 = 2 Ω, and the second time the resistor of the resistance R2 = 0.5 Ω. In both cases the resistor uses up the power of 2W. What is the internal resistance of the battery? What is the driving voltage of the battery?

Homework Equations



P= V*I
V= R*I
P= R*I²
P= V²/ R

The Attempt at a Solution



- Now I derivate three general equations:

1) V(0)= R(1)I(1) + R(0)I(1)
2) I(1)= V(0)/ (R(1) + R(0))
3) I(2)= V(0)/ (R(2) + R(0))

- Now I plugged these three equations in the power formula and got:

P= R(1)I(1)²= R(1)*[V(0)²/ (R(1) + R(0))²]
V(0)²= [P*(R(1) + R(0))²]/ R(1)

P= R(2)I(2)²= R(2)*[V(0)²/ (R(2) + R(0))²]

P= R(2)* [(P*(R(1) + R(0))²)/ (R(1)* (R(2) + R(0))²)]
1= [R(2)/R(1)]*[ (R(1) + R(0))²)/ (R(2) + R(0))²)]
R(2)/R(1)= (R(1) + R(0))²)/ (R(2) + R(0))²)
sqrt(R(2)/R(1))= (R(1) + R(0))/ (R(2) + R(0))
sqrt(R(2)/R(1))* (R(2) + R(0))= R(1) + R(0)
R(0)*(sqrt(R(2)/R(1))) – 1)= R(1) – ((sqrt(R(2)/R(1)))*R(2))
R(0)= [R(1) – ((sqrt(R(2)/R(1)))*R(2))]/ [sqrt(R(2)/R(1))]
R(0)= 1/3 Ω

V(0)²= [P*(R(1) + R(0))²]/ R(1)
V(0)²= 2.33 V

Are my calculations correct?
Thank you for helping!:smile:
 
Physics news on Phys.org
I am getting different answer.
P= R(1)*[V(0)²/ (R(1) + R(0))²] = R(2)*[V(0)²/ (R(2) + R(0))²]
Cancel V(0)^2 from both and rearrange the terms. You get
R(1)/R(2) = [R(1) + R(0)]^2/[R(2) + R(0)]^2
Substitute the values of R(1) and R(2) and solve for R(0).
 
OK, I rewrote my equations and recalculated and this are my new results:

R(0)= 1 Ω
V(0)= 3 V

Are my calculations correct?

Thank you for helping!:smile:
 
Yes. Your calculations are correct.
 
Thank you for reviewing and all the help!:smile:
 
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top