In the equation for wave velocity (v = λ/T), the symbol λ represents the wavelength of the wave, not the change in distance. The use of λ instead of Δd (delta distance) is to specifically indicate the characteristic length of one complete cycle of the wave.
The symbol Δd is typically used to represent a change in distance or displacement. It is used in equations where we are interested in measuring the difference between two distances or the change in position.
On the other hand, the symbol λ (lambda) specifically represents the wavelength, which is the distance between two consecutive points in a wave that are in phase with each other. It is a characteristic property of the wave and represents the length of one complete cycle of the wave.
By using λ in the equation v = λ/T, we are explicitly referring to the wavelength of the wave rather than a change in distance. This equation relates the wave velocity (v) to the wavelength (λ) and the period (T) of the wave.