Finding magnitude of external field from two magnetic fields

AI Thread Summary
To determine the magnitude of the external magnetic field needed to cancel the fields from two parallel wires carrying equal currents of 20 amps in opposite directions, the magnetic field (B) created by one wire can be calculated using the formula B = (4π x 10^-7)(I) / (2π x r), where r is the distance between the wires (0.019 meters). The resulting magnetic field strength from one wire is approximately 0.00021 Tesla. To achieve cancellation, an external field of equal magnitude but opposite direction is required. The total repulsion force between the wires is not needed for this calculation, as the focus is on balancing the magnetic fields. The correct approach is to use the calculated magnetic field from one wire to find the necessary external field.
rosstheboss23
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Homework Statement


I was wondering how would you determine the magnitude an external field needed to cancel two magnetic fields in two wires? In this instance the currents of the two wires are in opposite directions...so I know there is a repulsion force.
The currents in both wires are equal to 20 amps apiece
The wires are parallel to each other and are 0.019meters apart.


Homework Equations


Going about this problem I thought this would be useful F(magnetic)= (Current)(Length)(Magnetic field)
Also I thought this would be useful B= (4piE-7)(I) divided by (2pie X r)


The Attempt at a Solution


When I tried to plug in the values for B I got 0.000210526 for the magnetic field in one wire. If I double this I get 0.000421053 for the total force of repulsion. Would this be the correct way of approaching the problem.
 
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No, just go with the 0.00021. That's the magnetic field due to one wire, at the location of the other wire.
 
Thank you. I really appreciate your help.
 
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}...
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