What is the magnitude of the magnetic field?

AI Thread Summary
The discussion revolves around calculating the magnitude of the magnetic field affecting a rectangular coil with specific parameters. The formula for torque is provided, and the correct approach to find the magnetic field involves using the equation B = torque / (n * i * A * sin(theta)). A key point raised is the necessity to convert the area from cm² to m² and to correctly interpret the angle theta, which should be the angle between the normal to the coil and the magnetic field, suggesting the use of sin(72°) or cos(18°) for accurate calculations. The user expresses frustration with consistently arriving at an incorrect answer, indicating a potential misunderstanding of these concepts. Clarifying these details is essential for solving the problem accurately.
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What is the magnitude of the magnetic field??

Homework Statement



A small rectangular coil composed of 37 turns
of wire has an area of 36 cm2 and carries a
current of 0.8 A. When the plane of the coil
makes an angle of 18◦ with a uniform magnetic
field, the torque on the coil is 0.07 Nm.
What is the magnitude of the magnetic
field? Answer in units of T.

Homework Equations



Torque = n*i*A*B*sin(theta)
B= torque/(n*i*A*sin(theta))
n is the number of turns

The Attempt at a Solution



what i did is that i plugged all the given values .. but i keep get the wrong answer .. i don't know where is my mistake

thanx in advance
 
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Did you convert the area to m2?
 


theta is the angle made between the normal to the coil to the magnetic field. Think about it, if the coil is parallel to the magnetic field (theta = 0), the torque is maximum (the forces on the wires are directly opposite), as opposed to if you used sin 0 = 0, that is torque = 0. So you have to use sin 72 or cos 18 in the equation.

I don't even know if that's the problem, but I hope it helps.
 
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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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