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electrika
electrika
Student
College - Freshman

A disc is radial crossed, through sliding contacts, by an electrical current I=4A. The disc is set perpendicullar on a magnetic field, B=20mT.

The disc radius R=50mm

1. Calculate the power of engine, knowing the speed is n=5rot/s.

2. Find the torque moment.

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Posted by electrika on Saturday July 4, 2009 at 6:20 AM and tagged with power of engine, science, sliding contacts, speed, torque moment..

Answers:

  1. giorgiana1976
    giorgiana1976 Teacher
    Doctorate

    eNotes Editor

    We'll take an infinitesimal element"dx", of radial current. This element is placed at the distance "x" from the axis of the disc.The elementary force which is acting on the current segment:

    dF=l*B*dx

    The power developed by this force is:

    dP=dF*v=l*B*dx*2*pi*n*x

    If we'll inegrate the relation above:

    P=Integral (dP)=Integral(l*B*2*pi*n*x*dx) =

    =l*B*2*pi*n*(x^2/2) from 0 to R=pi*n*R^2*I*B=3.14mW

    The elementary moment of the elementary force dF is:

    dM=dF*x=(l*B*dx*x)

    M=Integral (dM)=I*B*Integral (x*dx) from 0 to R=

    M=(1/2)*I*B*R^2=0.10mN*m

    The result could be obtained from the relation P=M*omega

    omega=angular speed

    M=P/omega=(pi*n*R^2*l*B)/(2*pi*n)=(1/2)*I*B*R^2

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    Posted by giorgiana1976 on Wednesday July 8, 2009 at 10:34 AM