Doppler Shift Formula

What is the Doppler Shift Formula?

The Doppler Shift Formula is a mathematical equation used to determine the frequency shift of a wave. It is named after Christian Doppler, the Austrian physicist who first described the phenomenon in 1842. The formula calculates the difference in frequency between the original wave and a new wave observed by an observer in motion relative to the source of the wave.

The formula is represented as Δf/f = v/c, where Δf is the difference in frequency, f is the original frequency, v is the observer’s velocity, and c is the speed of the wave. This formula can be used to calculate the Doppler shift for any type of wave, including sound waves, light waves, and radio waves.

Understanding the Science Behind It

The Doppler Shift Formula is based on the idea that when an observer is moving towards a source of waves, the frequency of the wave appears to increase. Conversely, when the observer is moving away from the source of waves, the frequency appears to decrease. This phenomenon is known as the Doppler effect.

The Doppler effect occurs because the motion of the observer changes the effective wavelength of the wave. The observer perceives the wave as having a shorter wavelength when moving towards the source, and a longer wavelength when moving away from the source. The formula mathematically captures this relationship between the observer’s velocity, the speed of the wave, and the observed frequency.

Applications of Doppler Shift Formula

The Doppler Shift Formula has a wide range of applications in various fields. In astronomy, it is used to measure the velocity of stars and galaxies by analyzing the shift in the frequency of light emitted by them. In medicine, it is used to measure the velocity of blood flow and the motion of organs within the body using ultrasound waves. In radar and sonar technology, it is used to detect the motion of objects by analyzing the frequency shift of reflected waves.

Example Scenarios and Calculations

Here are two scenarios to illustrate the use of the Doppler Shift Formula:

  1. A police car is traveling towards a stationary observer with a siren that emits a sound wave at 500 Hz. If the speed of sound is 340 m/s, and the police car is traveling at 30 m/s, what is the frequency of the sound wave observed by the observer?

Δf/f = v/c

Δf/500 = (30/340)

Δf = (500 * 30)/340

Δf = 44.12

The frequency observed by the observer is 500 + 44.12 = 544.12 Hz.

  1. A star emits light at a frequency of 5.5 x 10^14 Hz. If the observed frequency of the light is 5.6 x 10^14 Hz, what is the velocity of the star relative to the observer?

Δf/f = v/c

(5.6 x 10^14 – 5.5 x 10^14)/5.5 x 10^14 = v/3 x 10^8

v = (3 x 10^8 * 0.01818)

v = 5.45 x 10^6 m/s

The velocity of the star relative to the observer is 5.45 x 10^6 m/s.