Calculating Fields near Wires and Solenoids

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Calculating Fields near Wires and Solenoids

You will already know that the magnetic field near a current gets weaker as you move further away from the current.

The magnetic field strength is inversely proportional to distance:

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The magnetic field strength is proportional to current:

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Combining these relationships gives:

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where the constant depends on the shape of the conductor.

Field around a straight wire:

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Where:

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I = current throught the wire (A)

r = distance from the conductor (m)

Field in a long straight solenoid:

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Where:

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n = number of turns on the coil per metre (m-1)

I = current throught the solenoid (A)

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The strength of a magnetic field can be found using a device called the Hall probe. It works on a principle based on the Hall effect.

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