The apparent change in light wavelengths due to motion is called which phenomenon?

The apparent change in light wavelengths due to motion is called which phenomenon?

• A. Refraction
• B. Diffraction
• C. Doppler effect
• D. Interference

Answer: (C)

This is the Doppler effect: a change in the observed wavelength (and frequency) of light that results from relative motion between the light source and the observer. Because light travels at a constant speed in vacuum, shifting how often wave crests reach you changes the frequency you measure. When the source moves toward you, the crests arrive more frequently, boosting the observed frequency and shortening the wavelength (blueshift). When the source moves away, the crests arrive less frequently, lowering the observed frequency and lengthening the wavelength (redshift). This is different from refraction (bending due to entering a medium with a different speed), diffraction (bending around obstacles or through openings), and interference (the combination of overlapping waves producing patterns). The key idea is that relative motion alters the observed wavelength and frequency of light.

This is the Doppler effect: a change in the observed wavelength (and frequency) of light that results from relative motion between the light source and the observer. Because light travels at a constant speed in vacuum, shifting how often wave crests reach you changes the frequency you measure. When the source moves toward you, the crests arrive more frequently, boosting the observed frequency and shortening the wavelength (blueshift). When the source moves away, the crests arrive less frequently, lowering the observed frequency and lengthening the wavelength (redshift). This is different from refraction (bending due to entering a medium with a different speed), diffraction (bending around obstacles or through openings), and interference (the combination of overlapping waves producing patterns). The key idea is that relative motion alters the observed wavelength and frequency of light.