Determining the Transformation Factor of a Tangent Galvanometer

Determination of the conversion factor of a tangent galvanometer

Instrument

Tangent galvanometer; 0~2A ampere ratio 0~10Ω variable resistance box; 2V battery; plug switch; reversing switch.

Experimental procedures

The installation circuit is shown in Figure 28/3. T is a tangent galvanometer, which is connected to the terminal marked with "2" with a flexible wire. "2" means that two turns of coil are used. K1 is a push button switch; R is a rheostat; A is an ammeter; K2 is a conversion switch; and B is a battery.

The galvanometer should be placed away from other equipment so that the effects of (i) the current flowing through R and other components and (ii) the magnetic effect caused by the ammeter magnet can be neglected. These two points are also the reason why the galvanometer is connected to the circuit with twisted braided wire (so that the magnetic effects of the current flowing into the galvanometer and the current flowing out of it are equal and opposite).

Rotate the galvanometer so that its coil plane is in the geomagnetic meridian plane. The pointer reading is zero. Pass current and adjust R to make the galvanometer pointer deflect 30°. Record the reading and current I at this time. Reverse the current without changing its magnitude and record the corresponding reading again. Increase the current to make the deflection change by 6°. Repeat the observation and gradually increase the current. Take four readings for each I value. Take a total of six sets of readings, arranged in the order of the deflection angle range from 30° to 60°.

Record the number of turns in the coil and measure its diameter.

Data recording and processing

Record the diameter and number of turns of the coil, and tabulate the observed values ​​of I and θ as follows
Plot tgθ-I and deduce the value of the conversion factor from the curve. Calculate the conversion factor based on the best set of data and explain the accidental error of the result.