Observed Frequency

Definition

The observed frequency refers to the frequency at which an observer perceives a sound wave or light wave due to relative motion between the source and observer.

Analogy

Imagine you are standing on a sidewalk while cars pass by. As each car approaches you, its engine sounds higher-pitched (higher frequency), but as it moves away from you, its engine sounds lower-pitched (lower frequency). This change in pitch is similar to how observed frequency changes due to relative motion.

Related terms

Doppler Effect: The Doppler effect describes how the perceived frequency of waves changes when there is relative motion between the source of waves and an observer.

Redshift/Blueshift: Redshift refers to an increase in wavelength (and decrease in observed frequency) of light waves due to objects moving away from us. Blueshift refers to a decrease in wavelength (and increase in observed frequency) of light waves due to objects moving towards us.

Sonic Boom: A sonic boom occurs when an object moves faster than the speed of sound, creating shockwaves that produce a loud noise.