An elementary book on electricity and magnetism and their applications . ted. Then an application of one of the rules givesthe direction of the current. This means is very commonly used in electrical manufactur-ing establishments and intesting laboratories. 67. Solenoids. By applyingone of the rules given in sec-tion 66, we see that if a wirecarrying a current is passedabove a magnetic needle, andthen is turned back and passedbelow the needle, both the top and the bottom branches of thecurrent tend to deflect the needle in the same direction, so thatthe effect on the needle is increased. (See
An elementary book on electricity and magnetism and their applications . ted. Then an application of one of the rules givesthe direction of the current. This means is very commonly used in electrical manufactur-ing establishments and intesting laboratories. 67. Solenoids. By applyingone of the rules given in sec-tion 66, we see that if a wirecarrying a current is passedabove a magnetic needle, andthen is turned back and passedbelow the needle, both the top and the bottom branches of thecurrent tend to deflect the needle in the same direction, so thatthe effect on the needle is increased. (See Fig. 48.) If thetwo branches are equally near the needle, they act upon it withequal force, and thus the total force on the needle is coiling the wire about the position of the needle, each ad-ditional turn will cause an additional deflecting force. Inthis way the magnetic effect of a current may be greatly multi-plied. It has already beensaid that the magnetic forceat a given point due to a cur- Fig. 48. — Magnetic needle placed atcenter of coil of Fig. 49. Loose solenoid with its linesof force. rent near it depends upon the strength of the current. We now see that when a current is coiled around a point, the force depends upon the strength of the current multiplied by the number of turns in the coil. This product of the current by the turns is usually called ampere turns.^ When a wire carrying a current is coiled into a ring or helix,the lines of force which surround each turn seem to join to- ELECTROMAGNETISM 93
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
