Direction and magnitude of the current

AI Thread Summary
The discussion focuses on determining the direction and magnitude of current in a circuit with a 1.00 kΩ resistor and a 250 V source. Participants suggest applying Kirchhoff's loop rule to analyze the circuit, considering the combination of 4R and 3R resistors in parallel to simplify calculations. There is confusion regarding the values of x and y in the equations used to find the currents I1 and I2, as well as the total resistance in the modified circuit. Clarification is sought on how to accurately represent the current through the combined resistors. The conversation emphasizes the importance of correctly applying circuit analysis principles to solve the problem.
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Homework Statement


Taking R = 1.00 kΩ and ε = 250 V in the figure, determine the direction and magnitude of the current in the horizontal wire between a and e.
http://img5.imageshack.us/img5/7250/img001nkm.th.jpg


Homework Equations


Kirchhoff´s law


The Attempt at a Solution


I must try to apply Kirchhoff´s loop rule to both rules?
 
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Yes, all three loops. Or perhaps you could combine the 4R and 3R in parallel to get a simpler circuit with only two loops. Once you know I1 and I2, it should be easy to find I in the original circuit.
 
I think it will be done with 4R and 3R in parallel. But how can i have the value of the new R?
 
Last edited:
If i have the new value of R i could find I1 and I2, like this:
(xR)I1+(yR)I2=250
and
(xR)I1+(yR)I2=500

I think it will be the solution, but the problem is that i can't find the new value of x and y if i combine the 4R and 3R in parallel to get a simpler circuit with only two loops.
Any help? Thanks
 
The 4R and 3R (4000 and 3000 ohms) are in parallel. You must use the formula for the resistance of two resistors in parallel.

I don't understand what your x and y represent.
It seems to me the current through the combined resistors would be I1 + I2, so the equations will each have one more term than you have shown.
 
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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}...
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