Science – Sound Waves, Light and Doppler Effect

Posted in Science on the 04.02.2012

What is Doppler effect?


Doppler effect is when the frequency of a light wave or sound depends on the speed between the observer and source. An example of this can be an ice cream truck. When the ice cream truck approaching, meet our ear in several variations in the wave peaks per second than when it moves away. You hear that is first and foremost a loud sound when the ice cream truck approaching, but when it runs past the sound is softer and deeper.

Dopplereffektens detection

Christian A. Doppler

Christoph Hendrik Diederik Buys Ballot

Armand-Hippolyte Fizeau

Doppler effect was proposed in 1842 by Christian A. Doppler. He mentioned this in the monograph Über das Licht farbiger where Doppelsterne und andere agree Gestirne Dec Heaven. Following this view, several scientists, curious, and the first to take the initiative to test out this was no mention Christoph Hendrik Diederik Dutchman Buys Ballot. The Dutch scientist tested it out using the trains and horn blowers. During this experiment, he explained that the pitch was higher when the train approached, and lower when it went. All this he explained as early as 1845. But this did not stop for the Doppler effect, the French Armand-Hippolyte Fizeau discovered something without any bearing on the Doppler and Buys Ballot’s theory in 1848. The difference between the discovery of the French scientist was that he discovered the process of electromagnetic waves. Therefore, this effect is sometimes called “effet Doppler-Fizeau” in France.

Dopplereffektens tasks


Blue and red

Shifts of galaxies

Doppler effect measure speed in heavenly synslinjens direction. This effect is really great meaning in astronomy. If spectral lines are thrust against the blue (higher frequency) coming up are the same lines shifted towards the red (lower frequency) then remove the body from him. We can say that the amount of creep increases with speed. The theory of the redshift increases with increasing distance and that the lines in the light of galaxies is largely shifted towards lower frequency, is proved by the Doppler effect by means of the distant galaxies is pushed away from our solar system with a high speed. In a different way, we can say that the universe expands.

The use of the Doppler effect



Doppler offset and spectral

The use of the Doppler effect of light depends on the fact that the Spectral range of stars is not continuous. They have absorption lines at very precise frequencies that correspond to the energies needed to rise electrons in various elements from one level to another. Absorption lines are not always at the frequencies they are in the spectral range of a stationary light source-rooted. This is seen by the Doppler effect.

Dopplerforsyvningen tend to be different from atom to atom because spectral lines of atoms in disordered often a thermal (defined as the sum of measurable and latent heat) activity and also a certain addition to its width. Called dopplerforbredning. How can the Doppler effect is used to determine the speed of the individual nuclei or atoms.

Dopplerforskyvnings practice

Radar waves


Doppler shift is practiced by radar waves to best speed of such aircraft, cars and rockets. Because of the Doppler effect from radar waves thrown back by an object moving towards the transmitter, we obtain a higher frequency than the wave that was sent out. Object speed can be determined very punctual by comparing these two frequencies.

Waves as the source emits not change frequency. This is well explained in wikipedia: Some throw balls at you. Every second person throws a new ball in the head, and we assume that the ball skimming through the air at a constant speed. Is the ball thrower will have a ball in the head every second. Is ball thrower on a cart that rolls towards you, he will be a little closer for every ball he throws. Each ball is therefore a slightly shorter distance to cover. And it will go a little less than a second between each ball that hits you in the head. And it feels as if the pitcher throws ball more often. The opposite is the case if the shooter rolls ball from you. In reality it is the wavelength of that change. As a consequence changes the perceived frequency. Retrieved from .. (

Doppler and medicine


Doppler Ultrasound

An echocardiogram (cardiac ultrasound) can provide information with no limits on the movement frequency and directions in cardiac tissue and blood. This is done using Doppler ultrasound. Speed measurement makes it possible to determine the function of heart valves, cardiac stroke volume to calculate and find openings in the walls of the heart. One can also measure the frequency of the cardiac muscle with stretch using vevsdoppler.

Sound waves

How sound waves are formed?

Densification and dilutions

When a source turns back and forth, and initiate changes in the air formed waves. These waves are called sound. When the sound source turns in one direction will air molecules on the side where the sound source turns to be mashed together. Then it creates a densification. And when it turns later in the opposite direction, release the left a dilution of air molecules. There is constant new dilutions and densification in the air that spreads outward. Air molecules fluctuate back and forth by wave direction. The distance between two densification or between two dilutions is equal to the wavelength of a sound wave.

Light waves

Electromagnetic waves


Light is electromagnetic radiation, ie waves that do not need matter to travel in. Em radiation is not something we can touch so that the air in sound waves. When we talk about light we can use both the word waves and radiation. Electromagnetic radiation is at wavelengths shorter than 1mm. But when the wavelength is larger than 1mm, we use the term waves. For example, microwaves and radio waves.