Electricity for public schools and colleges . e presence ofcopper and of other conducting masses on magnetic needlesoscillating near them. If a needle oscillate very close over acopper disc, and still more if it oscillate between two copper discs, 364 ELECTRICITY CH. XXII. it will very soon come to rest. This is due to the induction ofcurrents in the copper, these currents being such as to oppose thatmotion of the needle which is the origin of the induction. In the figure we have a copper disc caused to rotate with greatvelocity under a magnetic needle; a sheet of glass between thetwo obviates
Electricity for public schools and colleges . e presence ofcopper and of other conducting masses on magnetic needlesoscillating near them. If a needle oscillate very close over acopper disc, and still more if it oscillate between two copper discs, 364 ELECTRICITY CH. XXII. it will very soon come to rest. This is due to the induction ofcurrents in the copper, these currents being such as to oppose thatmotion of the needle which is the origin of the induction. In the figure we have a copper disc caused to rotate with greatvelocity under a magnetic needle; a sheet of glass between thetwo obviates any disturbance due to air-eddies caused by therotating disc. The needle is deflected in the direction of rotationof the disc, and will, if the velocity be great enough, finally rotatealso. This motion of the needle is not difficult to explain. Inconsequence of the rotation of the disc in the magnetic field dueto the needle, currents are induced in the former. These currentsare in such a direction that they oppose the relative modon of disc. and needle. They would be induced equally if the disc werestationary and the needle rotated. We have thus a reactionbetween needle and disc that tends to stop the relative motion ;and so, if the needle be free to move, it will be urged round in thesame direction as the disc. If slits be cut radially these interferewith the induced currents, and therefore with the actions described;but if they be cut in circles whose centres he on the common axisof rotation of disc and of needle, their presence makes much lessdifference. § 3. Continuous Current Collected from Barlows Wheel.—In the figure the dots represent a field of force, supposed to berunning down into the plane of the diagram. The circle is acopper disc, revolving in the direction of the arrow. O B C A O CH. xxiT. ARAGOS DISC AND RUHMKORFFS COIL 365 is a circuit, of which OCA is a wire connected at O with theaxis of the disc, and having shding contact with the edge of thedisc at A; t
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Keywords: ., bookcentury1800, bookdecade1890, bookpubl, booksubjectelectricity
