You are strapped into a rear-facing seat at the middle of a long bus accelerating: from rest at about (a rather violent acceleration for a bus). As the back of the bus passes a warning sign alongside the street, a red light of precisely wavelength on the sign turns on. Do you see this precise wavelength? Does your friend silting at the front of the bus see the wavelength you see? How could the same observations be produced with the bus and sign stationary?

The acceleration$a=10\text{\hspace{0.33em}m}/{\text{s}}^2$,

The wavelength,$\lambda =650\text{\hspace{0.33em}nm}$.

The Doppler effect can be seen when the source wave moves concerning the observer. The Doppler effect defines the change in the frequency of light concerning the observer produced by the moving source.

Due to the Doppler shift of your velocity relative to the observer, you will not see the precise$650\text{\hspace{0.33em}nm}$ wavelength. Your friend will not see the same wavelength as you can because light takes time to travel, and the speed of the bus has increased due to increased acceleration.

The same observations can be reproduced because whenever the bus goes up and down due to the gravitational field, the wavelength of the light beam goes down and up, respectively.

Hence the you will not see the precise$650\text{\hspace{0.33em}nm}$ wavelength and your friend will also not see the same wavelength.