Let s talk about the Doppler effect! How to explain the Doppler effect

An increase in frequency causes the sound to pitch up. The frequency determines the pitch of the sound.

Categories: Education Science >> Admission >> College Entrance Examination Problem Description:

When the frequency of the sound is getting lower and lower when the person hears it, the possible reason is ( )aBoth the sound source and the person are stationary, and the frequency of the vibration of the sound source is getting lower and lower.

b.People are still. The sound source moves in a straight line at a uniform speed away from the person, and the frequency of the vibration of the sound source remains unchanged.

c.When the person is stationary, the sound source moves in a straight line at a uniform acceleration away from the person, and the frequency of the vibration of the sound source remains unchanged.

d.When the person is stationary, the sound source moves in a straight line at a uniform deceleration away from the person, and the frequency of the vibration of the sound source remains unchanged.

Isn't BC the same as Stir Huna? It's all far away from people, and the frequency has changed.

Analysis: ac

B is not the same as C.

B means that the frequency that the person does not hear is lower than the original frequency of the sound, but remains the same, and C means that the frequency that the person hears is lower than the original frequency of the sound, and it is getting lower and lower.

d means that the frequency heard by a person is lower than the original frequency of the sound, but gradually becomes larger, and does not exceed the original frequency of the sound.

The Doppler effect was discovered by Christian Doppler. It refers to the fact that whether it is a wave of water, a wave of sound, or a wave of light, its frequency and wavelength will change depending on the relative velocity of the wave source and the observer.

Let's take a simple example. Imagine a stationary boat docked on the surface of a lake, and someone rides on the boat and rows the oars to paddle the surface of the water at a specific speed at a certain interval of time, causing it to make water waves. A person on the surface of the water can observe that the waves of water will come towards him at a specific speed at a certain interval of time.

Let's assume that the boat is heading towards a person dressed in blue on the other side of the lake, and that the person in the boat is making water fluctuations at the same speed at the same time interval. However, when the boat is moving towards the other side of the lake, the person dressed in blue will feel that the time interval between the water waves is shorter and faster, that is, they can see that the wavelength that causes the water waves has become shorter. But the opposite phenomenon will be observed by the person in red clothes on the side that is far away from the ship, and he will notice that the time interval between the arrival of the fluctuations becomes larger and the speed is slower.

In other words, water waves with longer wavelengths can be observed. A similar effect occurs when the ship itself does not move but the observer does.

It's the same when you think about water waves instead of light waves. Fluctuations in all forms have roughly the same effect, which is known as the Doppler effect.

Keep a time diary tomorrow for easy review).

There are three formulas for calculating the Doppler effect:

1. Longitudinal Doppler effect (i.e., the velocity of the wave source and the connection between the wave source and the receiver are collinear): f'=f[(c+v) (c-v)] 1 2), where v is the relative velocity of the wave source and receiver. When the wave source approaches the observer, v is normalized, which is called a "violet" or "blueshift".

Otherwise, v is negative, which is called "redshift".

2. Transverse Doppler effect (i.e., the velocity of the wave source is perpendicular to the connection between the wave source and the receiver): f'=f(1- 2) (1 2), where =v c.

3. Universal Doppler effect (general situation of Doppler effect): f'=f[(1- 2) (1 2)] 1- cos), where =v c, is the connection between the receiver and the wave source to the direction of velocity.

The Doppler effect was proposed by the Austrian physicist and mathematician Christian Johann Doppler in 1842. The main content is that due to the relative motion between the wave source and the observer, the observer feels the phenomenon of a change in frequency.

This effect is also caused by fluctuating light, also known as the Doppler-Fizeau effect. In 1848, the French physicist Fizeau independently explained the wavelength shift from the star, pointing out the method of measuring the relative velocity of the star by this effect. Light waves differ from sound waves in that the change in the frequency of the light wave makes a person feel like a change in color.

If the star moves away from us, the spectral lines of light move in the direction of the red light, which is called a redshift. If the star moves towards us, the spectral lines of light move in the direction of violet, which is called a blue shift.