Absolute Measurements in Electricity and Magnetism

Capa
Macmillan and Company, 1884 - 207 páginas

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Página 44 - Therefore a conductor in a magnetic field, and carrying a unit current which flows at right angles to the lines of force, is acted on by a force tending to move it in a direction at right angles to its length, and the magnitude of this force for unit length of conductor, and unit field, is by the definition of unit current equal to unity. Applying this to our slider in which we may suppose a current of strength...
Página 43 - A current of this strength — that is, the current flowing in a wire of resistance one ohm, between the two ends of which a difference of potentials of one volt is maintained, — has been adopted as the practical unit of current and called one ampere. Hence it is to be remembered one ampere is one-tenth of one cgs unit of current. The amount of electricity conveyed in one second by a current of one ampere is called one coulomb. This unit although not quite so frequently required as the others,...
Página 157 - Instead of a single wire cutting the lines of force, a coil of proper dimensions (for many purposes conveniently of rectangular shape), the mean area of which is exactly known, may be suspended in the field with its plane parallel to the lines of force, and turned quickly round through a measured angle of convenient amount not exceeding 90°; or it may be suspended with its plane at right angles to the lines of force and turned through an angle of 180°. If n be the number of turns, A their mean...
Página 83 - Kirchhoff's second law. In any closed circuit of conductors forming part of any linear system, the sum of the products obtained by multiplying the current in each part taken in order round the circuit by its resistance is equal to the sum of the electromotive forces in the circuit.
Página 15 - ... centres of gravity" of magnetic polarity, should be determined by experiment : and allowances should be made for the magnitude of the arc of vibration ; the torsional rigidity of the suspension fibre of cocoon silk of the magnetometer in the deflection experiments, and of the suspension fibre of the magnet in the oscillation experiments ; the frictional resistance of the air to the motion of the magnet ; the virtual increase of inertia of the magnet due to motion of the air in the chamber ; and...
Página 12 - ... sling, and the box is turned round until the magnet is at right angles to the glass sides. A paper screen with a small hole in it is then set up at a little distance in such a position that the hole is in line with the magnet, and therefore in the same plane as the scratches. The magnetometer should be removed from its stand and this box and suspended needle put in its place. If the magnet be now deflected from its position of equilibrium and then allowed to vibrate round a vertical axis, it...
Página 39 - Hence if the intensity of the field we have imagined be i cgs unit, the distance between the rails i cm., and the velocity of the slider i cm. per second, the difference of potentials produced will be i cgs unit. This difference of potentials is so small as to be inconvenient for use as a practical unit, and instead of it the difference of potentials which would be produced if, everything else remaining the same, the slider had a velocity of 100,000,000 cms. per second, is taken as the practical...
Página 35 - ... these two radial lines when its point is at the corresponding division on the circle the adjustment is correct. When taking readings the observer places his eye so as to see the index just cover its image in the mirror bottom of the box, and reads off the number of degrees and fraction of a degree, indicated on the scale by the position of the index. Error from parallax is thus avoided. A mirror with attached magnets may be used, as in the magnetometer, instead of the needle and index. When this...
Página 9 - Let us consider the force acting on one pole, say the red pole of the needle. The red pole of the magnet exerts on it a repulsive force, and the blue pole an attractive force. Each of these forces has the value...
Página 43 - The work done by a force is equal to the product of the force and the distance through which the point of application is moved in the direction of the force...

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