Objective of Experiment. To use a search coil and CRO to investigate the magnetic field due to a straight wire carrying an alternating current

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Daswani

7A (27)

Magnetic fields around electric currents I – straight wire

Objective

To use a search coil and CRO to investigate the magnetic field due to a straight wire carrying an alternating current

Apparatus

Search coil, lateral and axial

CRO

Signal Generator

Ammeter

Low voltage power supply

PVC-covered copper wire

Rheostat

Slotted base

Perspex strip

Crocodile clips

Connecting leads        

Theory

The magnetic field due to the electric current in a long straight wire is such that the

field lines are circles with the wire at the centre.

The experiment should show that the magnetic field B at a point near a long straight wire is directly proportional to the current I in the wire and inversely proportional to the distance r from the wire.

This relation is valid as long as r, the perpendicular distance to the wire, is much less than the distance to the ends of the wire (i.e. the wire is long).  

The proportionality constant is written as μo/2π , thus,

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The value of the constant μo, which is called the permeability of free space, is

4π × 10-7 H m-1.

Procedure

The circuit was set up as shown below.

The signal generator was set to 5 kHz. The CRO was adjusted such that a trace was displayed. The frequency was changed to find out how the trace on the CRO was affected. The output of the signal generator was adjusted to produce a current. The time base was switched off and the length of ...

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