1. The problem statement, all variables and given/known data 2. Relevant equations Δφ = 2π (Δr/λ) 3. The attempt at a solution I understand how to get the phase difference, but is the equation for the combined wave (second last line) just something I should memorize? Also, where does the sin term go in the last line? And why are the units for amplitude "μV/m"? Aren't V/m the units for electric field?