200/60 = 3.33 ohms
3.33 ohms is the resistance of B.
This explanation may seem very long and complex, but if you will study it carefully you will find it to be very simple. When once you master it, you will be enabled to make many measurements of resistance which will add greatly to the interest and value of your experiments.
CHAPTER IX BELLS, ALARMS, AND ANNUNCIATORS
An electric bell may be bought almost anywhere for twenty-five cents, and from the standpoint of economy it does not pay to build one.
A bell is not a hard thing to construct, and the time and money spent will be amply repaid by the more intimate knowledge of this useful piece of apparatus which will be gained by constructing it.
The base is four inches wide and five and one-half inches long.
The magnets consist of two machine bolts, wound with No. 22 cotton-covered magnet wire. Fiber ends are fitted on the bolts to hold the wire in place.
The wire is wound on each of the magnets separately. Cover the cores with two or three layers of paper before winding on the wire. The ends of the wire are led through holes in the core ends. The ends of the bolts are passed through the yoke, and the nuts applied to hold them in place.