helmholtz galvanometer

and finding its reduction factor.

Trisha Banerjee @ 2010

A helmholtz galvanometer , like other galvanometers , is an instrument which can be use to measure dc current in the circuit.

It is an improved form of the tangent galvanometer . It consists of two equal coils placed coaxially at a distance equal to the radius of the either coil . The two coils are of the same radius on the same direction. The field at any point on the axis of the coil is equal to the sum of the magnetic field due to the individual coil.

it consists of two identical circular coils , each having several hundred turns in it, mounted coaxially at a distance equal to their radius. In the side of each coil , four terminals are provided . First of which is internally connected with the starting end of the coil , second is connected with the end of the second turn , third with the end of the 50th turn and fourth with the 500th turns. Wit the help of these terminals , equal number of turns of each coil can be connected in series to allow the same current to flow in the same direction.


Two coils of same radii

Axis and distance is measure in one direction.


Magnetic needle


A circular disc with a calibrated scale in degrees on it is mounted at the mid point of the common axis of the coils .A small magnetic needle with a pointer attached is capable of rotation in the horizontal plane .the disc is covered with a plane glass to avoid disturbance from outside . There are leveling screws are also provided to make the plane of the disc horizontal.


Connecting terminals.


rheostatcommutator

Dc supply

Trisha Banerjee @2010

Object:- To find the reduction factor of a Helmholtz galvanometer.

Apparatus:- Helmholtz galvanometer , battery , rheostat , commutator , ammeter .

Circuit diagram……


Procedure:-

a) Level the box of helmholtz galvanometer and see that magnetic needle is free to rotate in the horizontal plane.

b) Put the coil of the galvanometer in the maganetic meridian .c) Make the connection as shown in the figure. Allow some current to pass

in the galvanometer in one direction and observe the deflection of the pointer . Now, reverse the current with the help of commutator and see the deflection . If it is not equal to previous one , rotate the coils suitable till deflection due to direct and reverse are equal. Adjust the rheostat to get a deflection of 45 degree. Now take out the plug to make current zero.

d) Now move the distance from the dial in a one direction and see the deflection, and note the current from ammeter every time.


Precaution:-

a) The coil should be in magnetic meridian.

b) No magnetic materials and current carrying conductors should not be brought near the apparatus.


helmholtz galvanometer

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