How Do You Calculate the Phase of a Spherical Wave at Different Distances?

[aliaze1]

Homework Statement

A spherical wave with a wavelength of 2.0 m is emitted from the origin. At one instant of time, the phase at 4m is (pi) . At that instant, what is the phase at 3.5m? What is the phase at 4.5m at the same instant?

Homework Equations

∆Φ = 2π[(∆x)/λ]

The Attempt at a Solution

First i set 2 as ∆x and either 3.5 or 2.5 as λ which didn't work

Thanks in advance

 

[mgb_phys]

I think you should draw a sin wave ( either just by hand or in excel) and look at roughly how high it is at 4m then look just before (ie 3.5m) and just after (4.5m).
In introductory physics - never do the maths until you have amental picture and understand what sort of answer you are expecting. (ps this doesn't work for QM!)