Exam Help

Discussion in 'Homework Help' started by Hello, Dec 26, 2008.

  1. Hello

    Thread Starter Active Member

    Dec 18, 2008
    82
    0
    Can you please have a look at the attached file.

    I am having difficulty with Q6 part (v), not sure how to go about it.

    Any help is greatly appreciated.
     
    Last edited: Dec 26, 2008
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You know Ke, thus

    The voltage developed across the motor terminals, without the 5 ohm resistor connected, is

    E=Ke*ω

    You know Ke and ω thus you can calculate E (which is actually the back EMF when it is working as a motor).

    The armature resistance is 5 ohms and the load resistance (connected on the motor terminals) is also 5 ohms. Thus the total resistance is 10 ohms. Thus the current through the armature and the load resistance is :

    I=E/10

    Thus the power dissipated in the load is:

    P=(I^2)*5

    Assuming no losses, the torque is:

    T=P/ω
     
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