# How does the lead polarity work on a D'Arsonval galvanometer?

Following an illustration of D'Arsonval movement such as the following...

I notice that the N polarized part of the coil is connected to the positive lead and the S polarized part of the coil is connected to the negative lead. Why is the galvanometer configured this way? Does the meter always have to be configured this way?

• no, both N's & S's can be reversed with polarity – Sunnyskyguy EE75 Sep 27 '17 at 0:38

The orientation N and S of the movement electromagnet are determined by the direction of the current and the winding direction. This can be easily remembered using the right-hand grip rule.

Figure 1. The right-hand grip rule: with fingers wrapped in the direction of current flow the thumb points in the direction of the field (N). Source: OneSchool.

With a little thought it can be seen that the illustration in the question is correctly drawn and that the north pole of the momement is at the top.

I notice that the N polarized part of the coil is connected to the positive lead ...

Not quite right. The N isn't "connected" - it is a result of current flow and winding direction. There is no electrical connection as the wire is insulated.

Figure 2. Another D'Arsonval galvanometer movement diagram showing the springs. Source: Engineer's Edge

As current is increased the like poles repel introducing a turning moment which acts against a spring to give a rotation proportional to the current.