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

1. Nov 13, 2016

### jaus tail

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. Nov 13, 2016

### Simon Bridge

u(t)=1 when t>0 only.
integral is area under the graph - sketch the graph and see...

3. Nov 13, 2016

### LCKurtz

What are $T$ and $u(t)$ in your problem?

4. Nov 15, 2016

### jaus tail

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.