It is named after the German scientist Hermann Ludwig Ferdinand von Helmholtz.
Q.What is Helmholtz Galvanometer?
A. 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. .
Q. On what principle is Helmholtz Galvanometer based?
A. It is based on Tangent Law,which states that when two magnetic fields are acting perpendicular to each other, then for a given restoring field deflecting field is directly proportional to tangent of the angle made by resultant with restoring field.
Q.How does the field along the axis of coil vary?
A.The field F at distance x from the center of the coil of radius r is defines as:
where n is the number of turns and i is the current flowing through the coil.
Q.What is the magnitude of of field at the center?
A. For F at center,x=0,
Q.How can we increase the region of uniform field?
A.By using two identical coils placed co-axially at a distance equal to their radius.
Q.Define Tangent Law.
A. F=H tan θ,where H & F are mutually perpendicular magnetic fields.
Q.Why is it necessary to set the plane of coil in the magnetic meridian?
A.To make the magnetic field produced by the coils at ninety degrees to the horizontal component of Earth’s magnetic field.
Q.What is magnetic meridian?
A. A plane passing through the axis of magnetic needle freely suspended through it’s center of gravity & is at rest under Earth’s magnetic field.
Q.How is the error in measurement of deflection eliminated if the coil is not exactly placed in the magnetic meridian?
A.By passing current in one direction and then in reverse direction and then taking the mean of the four readings.we get deflection free from error.
Advantages of Helmholtz Galvanometer over Tangent Galvanometer.
Tangent galvanometer has uniform magnetic field only at the center while Helmholtz has it between the two coils.Helmholtz galvanometer is more sensitive.At the same current Helmholtz produces more deflection and field.