RYERSON UNIVERSITY

DEPARTMENT OF PHYSICS

TITLE OF EXPERIMENT: The Current Balance

           

 

Objective and Background:

  

        The objective of the experiment was to examine the magnetic force of repulsion between identical oppositely directed currents in parallel conductors.

        In 1820, Ampere observed that two parallel current carrying conductors interact with each other. Each conductor lies in the magnetic field of the other and experiences a force due to this field. The magnitude of this force is given by the equation below:

Where F is the force between two conductors in newtons, L is the length of parallel current carrying conductors in meters, d is the separation of parallel conductors in meters, I is the current that each conductor carries in amperes, K is   , and  is the is the permeability of free space.

Figure 1

       The graph of F against I² is a straight line with a slope which is equal to. Since the values of d and L are known, the value of K can be computed by the value of the slope. In this case that the conductors are surrounded by air, the value of K should be something near  NA -2 , which is the value for free space.

       Furthermore, the value for the equilibrium separation of the two bars can be calculated by the following equation:

where D is the difference in the scale readings, a is the distance between the knife edge and the bar, and b is the distance from the scale to the mirror.

Procedure and Observations:

Required Apparatus:

  1. Current balance with calibrated weights
  2. Telescope with support stand
  3. Caliper
  4. Power supply        
  5. Scale
  6. Measuring tape
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Figure 2: The experimental setup

        The current balance was set up on the laboratory bench with the current carrying bars extending in a north-south direction to eliminate the effect of the Earth’s magnetic field. The distance from the mirror to the scale was approximately 2 meters. The beam lift mechanism was designed to raise the beam, which caused the knife edges to come clear of their supports and then to return them to a certain position. This mechanism was used to return the knife edges back to their initial ...

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