. A text book of physics, for the use of students of science and engineering . Km. mis. -Force between parallel currents. LXXV KELVIN CURRENT BALANCE 971 long straight parallel wires carrying currents ix and ?2 in the samedirection. If the distance between them be r centimetres, thestrength of magnetic field at B due to A is 2ijr (p. 965). B beingsituated in this magnetic field experiences a force r xi2 = per centimetre of its length. By applying the left-hand rule (p. 968)it will be seen that the direction of this force is such that B is urgedtowards A. By a similar reasoning it may be shown
. A text book of physics, for the use of students of science and engineering . Km. mis. -Force between parallel currents. LXXV KELVIN CURRENT BALANCE 971 long straight parallel wires carrying currents ix and ?2 in the samedirection. If the distance between them be r centimetres, thestrength of magnetic field at B due to A is 2ijr (p. 965). B beingsituated in this magnetic field experiences a force r xi2 = per centimetre of its length. By applying the left-hand rule (p. 968)it will be seen that the direction of this force is such that B is urgedtowards A. By a similar reasoning it may be shown that A is urged towards Bivith a force 2i2i1/r per centimetre of its length. Further, we see that currents in the same direction attract each other,ind currents in opposite directions repel each other. When the circuits are not of such a simple form, it may not be,asy to calculate the force between them, but for any given positionhe force is always proportional to the product of the current current measuring instruments are based upon this Kelvin current balance.—The current to be measured passes throughix coils CLMABD in series (Fig. 909). A, B, C and D are fixed, while. and M are attached to an armvhich can rotate about an axis<H. A scale is also attached tohe arm and carries a weight Wvhich can be caused to slidelong this scale. The arm andcale must be so balanced that hen the weight W is on theero mark the beam is hori- ontal, as indicated by a ointer, when no current is owing. The coils are so con- ected that when the current flows, the forces between A and L,and L are in such a direction that L is pushed downwards. imilarly M is pushed upwards. The arm thus rotates. It is fought back to its equilibrium position by sliding the weight W • the right, which introduces a couple equal and opposite to that le to the current. The scale is so graduated that the movementthe weight upon it gives a direct reading of the current. This ale, however, is
Size: 1989px × 1256px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
