Il6 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



happens if the current is reversed in one coil ? What happens if the current is re- 

 versed in both coils ? Ans. 0.27 ampere. 



90. The spiral spring of a Seimens electrodynamometer is 

 twisted through an angle of 225 to balance the force action on 

 the movable coil when a current of 14 amperes flows through 

 the instrument. A twist of 160 is required to balance the force 

 action of a current which is being measured by the instrument. 

 Required the value of this current. Ans. 1 1.8 amperes. 



91. The horizontal component of the earth's magnetic field at 

 the needle of a sensitive galvanometer (Kelvin type) is o. 1 8 gauss, 

 and its direction is due north. It is desired to produce at the 

 needle a resultant magnetic field of 6.02 gauss intensity in a due 

 easterly direction. Find the distance and direction from the gal- 

 vanometer needle at which an isolated north magnet pole of 

 strength 600 gausses must be placed to produce the desired re- 

 sult. Ans. 57.6 cm., 6 20' west of north. 



