Describe with the aid of a diagram, an absolute method of measuring current.

Describe with the aid of a diagram, an absolute method of measuring current.

Current balance is based on principles of moments

The apparatus setup is as above, AB = AF, length BC = L and the current through the wire is A

The magnets provide a uniform magnetic field, B, perpendicular to wire BC.

At equilibrium when the frame BCEF is balanced

The force exerted on the wire = weight of the mass

BIL = Mg

I = Mg/BL

Sources of error

• Accuracy of length L
• Rigidity of the frame
• To avoid overheating, the current should be switched off as soon as measurements have been taken.
• Shield the set-up from the disturbance of wind.

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