Figure 1
Experiment 11 |
Magnetism |
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Figure 1 |
The magnetic field due to a current - carrying element of wire is given by the Biot-Savart Law. The magnitude of the magnetic field at a point P due to a current carrying element of wire of length dl is:
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(1) |
Constant mo is the permeability of vacuum.
The direction of the magnetic field, 
, is given by a right-hand
rule, perpendicular to both 
and
. Grasp the wire in your
right hand with your thumb in the direction of the current. The direction of
the magnetic field is in the direction in which the curled fingers are
pointing. For the example shown, the magnetic field is out of the
page.
The total magnetic field
due to a circuit of any shape may be found by adding up (integrating) all
the contributions by Equation 1 over the circuit.
Circular LoopFor a single circular loop of radius R carrying a current I, the magnetic field at the center is especially easy to determine because distance r and angle θ are constant for all dl (r = R, θ = 90°). Without requiring integration, the result
For the situation shown, the magnetic field at the center C is out of the page. |
Figure 2 |
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Square LoopFor a single square loop of side length L, the magnetic field at the center can be found in a similar way using integration.. The result is:
For the situation shown, the magnetic field at C is out of the page. The magnetic field at the center of a square loop is about 90% of a circular loop with the diameter equal to the length of square loop side. |
Figure 3 |
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SolenoidThe field inside a solenoid of a circular cross section where n is the number of turns per length is: |
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