Ques. How may the tangent galvanometer be used as an ammeter?
Ans. The strength of the current may be calculated in amperes by the formula given below when the dimensions of the instrument are known.
The needle is supposed to be subject to only the earth's magnetism and to move in a horizontal plane. The current is calculated as follows:
amperes = ((H × r)/N) tan x(1)
- H = constant from table below;
- r = radius of coil;
- N = number of turns of coil;
- x = angle of deflection of needle.
The constant H, given in the following table represents the horizontal force of the earth's magnetism for the place where the galvanometer is used. Each value has been multiplied by (2π )/10 so that the formula (1) for amperes is correct as given.
Table of Galvanometer Constants.--Values of H.
| Boston | .699 |
| Chicago | .759 |
| Denver | .919 |
| Jacksonville | 1.094 |
| London | .745 |
| Minneapolis | .681 |
| New York | .744 |
| New Haven | .731 |
| Philadelphia | .783 |
| Portland, Me. | .674 |
| San Francisco | 1.021 |
| St. Louis | .871 |
| Washington | .810 |
