![](data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 72 71" width="72"></svg>)
How is the speed of light measured?
At the beginning of the 17th century, Galileo used the method of measuring the speed of sound to measure the speed of light. He asked two people to carry a light with a baffle and stand about 1.6 kilometers apart. He asked the first person to turn on his light first and start timing at the same time. When the second person saw the first person's light on, he immediately turned on his own light. When the first person saw the second person's light on, he stopped timing, In principle, Galileo's method was right, but the experiment failed. This is because the speed of light is so great that it can go around the earth for more than one seventh of a second. It is difficult to measure the speed of light on the earth with the usual method of measuring the speed of sound depending on the conditions at that time, About 30 years after Galileo's death, Romer, the king of Denmark, pointed out in 1676 that the speed of light was limited in observing the eclipse of Jupiter
In 1834, British physicist Wheatstone used a rotating mirror to measure the duration of electric spark. He also wanted to use this method to measure the speed of light. At the same time, he also wanted to confirm whether the speed of light is greater in the medium with larger refractive index. Wheatstone's method of thinking was correct, but he did not complete it
He was the first person to measure the speed of light without astronomical constant or astronomical observation. He measured the speed of light by rotating gears. The measured speed of light was 342539.21 km / s, The difference between this value and the speed of light recognized by astronomers at that time is very small
Foucault is famous for his "Foucault Pendulum" experiment in the history of physics. In the study of measuring the speed of light, he used the method of rotating plane mirror to measure the speed of light. The measured speed of light is 29.8 × 107 M / s, and the error of the experiment can not exceed 5 × 105 m / s
On May 6, 1850, Foucault reported his experimental results to the Academy of Sciences, and found that the speed of light in water is smaller than that in air, which proved that the viewpoint of wave theory is correct
Michelson (American, a.a.michelson, 1852-1931) inherited Foucault's experimental idea and measured the speed of light at 299796 km / s with the method of rotating octahedral prism
RELATED INFORMATIONS
- 1. The speed of light is so fast, but how is it measured? Please, thank you
- 2. Will the measured speed of light be faster than the actual speed? The first thing to say is that my idea is definitely wrong, but I really don't know what is wrong, so I want to discuss it with you. Anyone who is interested can say two sentences If the distance between the earth and the sun is s, and we know that the time required for light to pass from the sun to the earth is t, then we can calculate the speed of light as S / T = C, but due to the tardiness effect, the distance between the earth and the sun will be reduced to s', so the calculated speed of light is v = s' / T, because s'
- 3. How to calculate the speed of light?
- 4. Is that faster than light? If a person goes against the light and the speed is V, then the speed of the photon relative to the person is C + V. although V is very small relative to the speed of light, it surpasses after all
- 5. Who, when and how does the speed of light work out? Who knows?
- 6. Do I reach the speed of light like this? Everyone knows that no one can reach the speed of light, but if I move to the left at half the speed of light and you move to the right at the same speed, then I'm not sure if you have reached the speed of light
- 7. Did Maxwell calculate the speed of light? I don't believe that one can calculate the speed of light by pure theory. Relativity only says that the speed of light is constant
- 8. The radius of the earth's orbit is often used in astronomy as a unit of length, called astronomical unit, to measure the distance between celestial bodies and the sun in the solar system
- 9. What is the sum of a number added, subtracted, and divided equal to 8.6?
- 10. It is known that the function f (x) is an odd function over [- 1,1] and monotonically decreases over the interval [- 1,0] If f (2m-3) + F (1-m) > 0, find the value range of real number M
- 11. How is the speed of light measured
- 12. I want to know How is the speed of light measured
- 13. There are about 100 billion stars in the Milky way. The distance between the nearest star Centaurus and the sun is about 4.22 light years (1 light year ≈ 9.46 × 10 12 km). How many years will it take to get to Centaurus by supersonic plane? (365 calculations per year, the speed of supersonic plane is 10350 M / s, so three significant numbers are reserved.)
- 14. The neighbor star is the closest star to the earth. The light from the neighbor star reaches the earth about 4.3 years ago. How many km is the neighbor star from the earth
- 15. Apart from the sun, the nearest stars to the earth are () A. Altair B, Vega C, Andromeda D, and the nearest star in Centaurus
- 16. The nearest star outside the solar system to the earth is called the neighboring star, which is 3600, 13000, 13000 kilometers away from the earth. Q: how long does it take for the light from the neighboring star to reach the earth? (it is known that the speed of light is 300000 km / s, which is calculated by 30000000 seconds per year. The results are expressed by scientific notation.)
- 17. The principle of laser rangefinder is understood. The distance can be calculated by calculating the time taken to receive the reflected laser, but what we don't understand is how to send it back? When a flashlight is used to irradiate a plane mirror three or four meters away, it will reflect back light, but when it is used to irradiate ordinary objects such as tables and stools (especially in the bright outdoor environment), it will not be seen that the light emitted by a flashlight will reflect back. Even the common laser lamp similar to a flashlight can not see the reflected light when it is three or four meters away in this environment, Is the reflection ability of the lunar surface so strong? How does the object reflect back the emitted beam or something else
- 18. At present, the measuring personnel use a laser rangefinder to send a pulsed laser beam to the moon and receive the reflected laser beam. They measure that the time for the laser to go back and forth is 2.54s. How many meters is the distance between the moon and the earth? (the speed of light in vacuum is 3 times 10 octave)
- 19. The laser rangefinder emits a laser pulse beam at the target The laser rangefinder emits a laser pulse beam to the target, receives the reflected laser beam, and measures the time taken for the laser column to go back and forth. Then the distance between the measured celestial body and the earth can be calculated. The distance between the earth and the moon is the eighth power of 3.8 * 10, Now the distance between the earth and the moon can be measured by laser rangefinder with an accuracy of plus or minus 10cm. Laser ranging technology is widely used in man-made earth satellite monitoring, geodesy and other aspects Known: Ask for: I will. Come on in~
- 20. How long does it take to fly from the earth to the moon