﻿730 Mr. G. Breit on the Effective 



Description of Pancake Coil. 



By a pancake coil is meant a coil whose wires are all 



wound in one plane in a spiral, as shown on the figure 



(see fig. 1). It will be supposed that the number of turns 



Fi£, 1. — Pancake coil. 



in the coil is large, that the turns are close together, and 

 that the thickness of the insulation is negligible. 



Thus the coil may be replaced by a disk on whose surface 

 the potential varies in the same manner as it does in the 

 coil. 



Notation. 



The radius of the pancake will be denoted by a. 

 Points in space will be referred to by cylindrical co- 

 ordinates 



with centre at the centre of the coil, aud with axis 

 perpendicular to the plane of the coil. 



Fig. 2. — Cross section of pancake coil by plane through diameter. 



P 



The meaning of these symbols is shown on fig. 



