How Is Magnetic Field Strength Calculated in a Balanced Wire Coil System?

[amy121212]

A small wire coil K is placed at the end of the mechanical balance and inserted between the poles of the magnet as shown on the picture. Number of turns in the coil N=200, coil’s cross-section S=1 cm2, the length of arm OA (between the pivot point and counterbalancing weight) l=33 cm. The system is balanced. Now, the coil is connected to the outside circuit (not shown) and a current I=30 mA is passed through the coil. In order to keep the balance, an additional weight of delta m=55 mg is placed on the counterbalance. Find the strength of magnetic field B at the coil’s location.





I really have no direction for this question

 

[jbsteele]

, but I believe that the magnetic field strength can be found by using the equation B = μ N I/l. The value of μ depends on the material of the magnet, so you will need to know that information in order to get the correct answer. In this equation, N is the number of turns in the coil, I is the current flowing through it, and l is the length of the arm OA. Plugging in the given values, we get B = (μ*200*30 mA)/33 cm = 18 μT.