We know from Ohms law that with the increase of resistance in a circuit, there is a decrease of current. This gives a simple method of approximately determining resistance, but it is not as accurate as the preceding method.

The battery of known E. M. E., the unknown resistance and a galvanometer are connected in series; the current passing will be indicated by the latter. The unknown resistance is then replaced with known resistance until the deflection of the needle is the same as with the unknown resistance.

Galvanometer resistance=say 100.

Battery resistance = say 0.

X= unknown resistance and R=known resistance.

A resistance of 320 w=deflection of 20 divisions or points.

An unknown resistance gave 30 points.

x = d1 / d (R + G) - G, or by arithmetic, x = 20/30 (320 +

100) -100=180 ohms, that is, X= known points divided by unknown points multiplied by the sum of the (known resistance and resistance of galvanometer) and then the resistance of the galvanometer subtracted from that.

x = d1 / d (R + G) - G, i. e. x = unknown points.