SHUDDEMAGEN. — DEMAGNETIZING FACTORS FOR IRON RODS. 243 



Dimensions of Iron Rod: Diameter = 5 mms. Length = 20 cms., so 

 that m = 40. 



Secondary Coil : 480 turns of fine wire. Length = 3 cms. Resist- 

 ance = 19.42 ohms. 



We therefore neglect the leakage of induction through the secondary 

 coil. If we have no extra resistance in the galvanometer circuit the 

 formula gives for the method of reversals : 



i. = m^ = ^ 3i = ,400 



T 8 ••_'-( 0.25 r4si i 0.00695 7T- 0.60 



This shows that we need no extra resistance for the secondary circuit. 

 Suppose we magnetize in a solenoid 31 cms. long and wound with 

 5 layers of wire, 1 13 turns in each layer. Then we have 



//' 



4 - 565 



10-31 



We get the following observations 



(No. of amperes) = 22.9 (amperes). 



giving the calculated results: 



