True / False: A moving wave source does not affect the frequency of the wave encountered by the observer

Yes and no.

If the source moves perpendicular to the line between the source

and the observer, then the observer observes the frequency and

wavelength equal to those emitted from the source.

If the source moves parallel to the line between the the source and

the observer, then the observer observes frequency/wavelength

different from those emitted from the source.