A) The rotation of Saturn's rings and of double stars has been detected using the phenomenon of Doppler effect.B) Megaphone and ear trumpet work on the principle of interference of sound.

In these two cases, two diametrically opposite sources of light are moving in opposite directios, one is moving towards the detector on earth and the other is moving away from the detector on earth. So apparent frequencies received by the detector, in both cases differ from the original frequency.