The Doppler effect is a phenomenon that occurs when there is relative motion between a source of waves and an observer. It causes a shift in the frequency of the waves as observed by the observer. The Doppler effect can manifest in various types of waves, including electromagnetic (EM) waves.
In the case of EM waves, such as light or radio waves, the Doppler effect affects the observed frequency of the wave. When a source of EM waves and an observer are in relative motion, the observed frequency of the waves can be different from the frequency emitted by the source.
If the source and the observer are moving closer together, the observed frequency of the EM waves will be higher than the emitted frequency. This is known as a "blueshift" because the shift is toward the higher-frequency end of the electromagnetic spectrum.
Conversely, if the source and the observer are moving away from each other, the observed frequency of the EM waves will be lower than the emitted frequency. This is called a "redshift" because the shift is toward the lower-frequency end of the electromagnetic spectrum.
The amount of frequency shift depends on the relative velocity between the source and the observer and the speed of light. For example, in the case of light, if a source is moving at a significant fraction of the speed of light relative to an observer, the Doppler effect can cause a noticeable shift in the observed frequency.
The Doppler effect in EM waves has practical applications, such as in astronomy. Astronomers can use the redshift or blueshift of light from celestial objects to determine their relative motion and deduce important information, such as the expansion of the universe or the presence of exoplanets.
Overall, the Doppler effect in EM waves manifests as a shift in the observed frequency of the waves when there is relative motion between the source and the observer.