FIELD ABOUT A WIRE 475 A MEANS OF SHOWING THE CIRCULAR MAGNETIC FIELD ABOUT A WIRE. BY WILLIAM BUTLER, McKrnley High School, St. Louis, Mo. Probably most of us have had trouble in making this clear to a class, because the current required for successful demon- stration is large. A trial made with the apparatus here described shows-that the lines may be made clear and distinct in the following way (see cut): A piece of double strength window glass was cut 4//xIO/’ and round ho^es drilled, as shown, by using the corner of a broken file, wet with turpentine and camphor, in the familiar way. As soon as the glass was pierced the hole was made round by using a rat tailed file in the same way. The glass was then put into a vise, and two wire nails were driven in the top of the bench, about 4" back of the -glass. A length of No. 24 D. C. C. magnet wire was then cut off,, and with help from an assistant was wound through the holes and around the nails, so as to make a coil of about 30 turns. Since the strength of the magnetic field depends on the num- ber of "amphere turns,^ and the resistance of the coil was found to be only 1.32 ohms, it is obvious that enough current may easily be sent through this coil to produce a strong field. Having a "battery charging" rheostat, and lib volt current available, about 8 amperes or current was sent through the coil. Upon sifting iron filings on the glass and tapping, a well-defined field was at once obtained. The diameter of the field on each side of the coil was about 3", and the lines at the center of the coil were parallel, as is usual.

A MEANS OF SHOWING THE CIRCULAR MAGNETIC FIELD ABOUT A WIRE

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FIELD ABOUT A WIRE 475

A MEANS OF SHOWING THE CIRCULAR MAGNETIC FIELDABOUT A WIRE.

BY WILLIAM BUTLER,

McKrnley High School, St. Louis, Mo.

Probably most of us have had trouble in making this clearto a class, because the current required for successful demon-stration is large.A trial made with the apparatus here described shows-that

the lines may be made clear and distinct in the following way

(see cut):A piece of double strength window glass was cut 4//xIO/’

and round ho^es drilled, as shown, by using the corner of a

broken file, wet with turpentine and camphor, in the familiar

way. As soon as the glass was pierced the hole was maderound by using a rat tailed file in the same way.The glass was then put into a vise, and two wire nails were

driven in the top of the bench, about 4" back of the -glass.A length of No. 24 D. C. C. magnet wire was then cut off,,and with help from an assistant was wound through the holesand around the nails, so as to make a coil of about 30 turns.

Since the strength of the magnetic field depends on the num-ber of "amphere turns,^ and the resistance of the coil wasfound to be only 1.32 ohms, it is obvious that enough currentmay easily be sent through this coil to produce a strong field.Having a "battery charging" rheostat, and lib volt current

available, about 8 amperes or current was sent through the coil.Upon sifting iron filings on the glass and tapping, a well-definedfield was at once obtained. The diameter of the field on eachside of the coil was about 3", and the lines at the center ofthe coil were parallel, as is usual.