Speed of light
How was the speed of light detected?
VEERESH S.M.
Karnataka
The earliest reference to the motion of light is traced to the Greek philosopher Aristotle who theorized in about 300 BC that light takes no time to travel from anywhere to anywhere although he also states that light goes from one point to another.
However after about 1300 years systematic experiments were carried out by AlHeytham in Egypt in 1020 AD using a device called Camera Obscura.
Camera Obscura is now known as the pin-hole camera whose working principle rests on the way different light rays travel from outside the camera to reach specific points on the screen at the back wall. AlHeytham’s logic used the idea of light to be taking finite time to travel finite distance.
However the attempt to estimate the speed of light yielded the value to be only more than the speed of sound which could be conceived with simpler experiments based on experience.
And, the idea was not pursued much farther until about Galileo’s time in the 17the century. Galileo’s estimate was based on very simple and rather inaccurate experiments and places light speed at ten times the speed of sound. However, Sir Isaac Newton gave his estimate of the speed of light to be about 112000000 m/s.
Subsequently, the Danish physicist Romer made an elaborate experiment using a telescope focused on the satellite Io orbiting Jupiter and estimated the speed of light to be about 227000000 metres per second.
In the 19th century AD, Fizzeu made an innovative improvement of Galileo’s experiment by using a mirror and a chopper wheel whose rotational speed could be precisely regulated and measured.
The value estimated by this experiment was 313000000m/s which is higher than the later value of 298000000m/s obtained from Foccoult’s modified experiment of Fizzeu. Michelson revised this value, through more precise experiments, to 299796000m/s.
Even this value has been now revised through extremely high precision experiments involving sensitive resonating cavities, wave guides and modern electronic circuits.
Although the more accurate values are important for good use by scientists, a value of 300000000m/s is sufficient for most applications.
H. K. SAHU
Scientific Officer
Indira Gandhi Centre for Atomic Research
Kalpakkam, Tamil Nadu
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
