I've just got into another book on electronics, but I've come into a wee problem with the maths, in one part.

Re. sinusoidal signals, I believe the equation to find the voltage is:

V=Asin2∏ft

That's fine with me. However, what I don;t quite understand is when you need to knwo the voltage at some arbitrary point in time, ie when t=0. The book says that the equation requires a phase in this equation:

V=Asin(2∏ft+ϕ)

What I don't understand is the need for the 2∏ft, as if t=0 then the whole bracket would come to θ!

I'm clearly missing something here, could someone explain this to me please?

The book is

**The Art of Electronics**, by

**Horowitz and Hill**.

Thanks in advance,

Sparky