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Homework Help: What is the power of unit step signal with magnitude A

  1. Nov 13, 2016 #1
    1. The problem statement, all variables and given/known data
    Find power of signal A u(t)
    A is constant like 5, 6 some value.

    2. Relevant equations
    Power is integration over -T/2 to +T/2 of [x(t)]2 dt
    The whole divide by T

    3. The attempt at a solution
    Power is integration over -T/2 to +T/2 of [A u(t)]2dt

    The whole divide by T

    So 1/T integral A2 dt...integral limits are -T/2 to +T/2
    This comes as 1/T A2 integral dt

    integral dt is t. limits are -T/2 to +T/2
    so integral dt = [T/2 - ( -T/2) ] which becomes T
    so Poewr is 1/T * A2 * T
    which gives A2

    But book answer is A2 /2
    Where did the divide by 2 come from?
  2. jcsd
  3. Nov 13, 2016 #2

    Simon Bridge

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    u(t)=1 when t>0 only.
    integral is area under the graph - sketch the graph and see...
  4. Nov 13, 2016 #3


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    What are ##T## and ##u(t)## in your problem?
  5. Nov 15, 2016 #4
    u(t) is unit function
    u(t) =1 for t > 0 or t =0
    u(t) = 0 otherwise.

    T is just a random time value. So -T to +T is symmetric about y axis.

    Ok now i get it. Since u(t) = 0 for negative time. the integral limit changes from (-T/2 to +T/2) to ( 0 to +T/2).
    Got it. Thanks.
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