New York University - PHYSICS V85.0012 >Current Balance Physics 2 Lab6 experiment

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Objective The purpose of this lab is to measure the permeability of free space. This will be done using a current balance apparatus and laser to verify the force between two wires, which is proport... ional to the permeability constant. Description Two wires carrying current near each other will experience force due to the other wire. The force that the wires feel is proportional to the products of the currents. The current balance apparatus has a wire that can pivot freely up and down, and a coil parallel to the freely moving wire right under it. These are connected in series, and therefore the same current passes through them both. But, the current is passing through them in opposite directions. This gives a net force of repulsions between the two. The laser is adjusted and two marks will be made, one for when two wire and coil are .1 mm apart and one for .2 mm apart. Weights will be added to the single wire, and since it moves freely, the current and repulsive force are adjusted to get the laser to hit the premade points. This is repeated with different weights and will be used to determine force as a function of current. Theory Two parallel wires are carrying current in opposite directions. This will lead to a net force of repulsion between the two. Since one wire is able to freely move up and down, the bottom coil will repel the top wire up. Force per unit length of one wire on another can be written as F= 2 μ0 IA IB 4 πD , where IA and IB are the currents in the two wires. This equation is for infinitely long wires. For wires of length L, force per unit length becomes F= 2 μ0 IA IB L 4 πD . Since in this experiment the two currents are the same and the coil has N = 10 turns, the equation is rewritten again as F=2 μ0 N I2L 4 [Show More]

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