How can we measure the speed of light?

Answer 1

I have measured the speed of light in a laboratory.

The equipment is like this: a laser will generate the light whose speed you will measure. The laser bounces off a polygonal array of mirrors (in my case there were 8 mirrors) which are attached to a high speed motor that can spin the mirror assembly at a known speed. When setting up the apparatus, make it so the laser bounces off one mirror, let's call it mirror 1, then goes a measured distance across the room and bounces off another mirror which is angled to aim the light beam to the NEXT mirror, mirror 2, and from there to a target where you see a dot of light.

Now start the mirrors spinning. Since they are turning, the light spot on the target will begin to shift in the direction of rotation (since the angle of the mirrors will have changed as the light was flying across the room and back). As the speed of rotation increases, the mirror assembly will eventually be rotating so fast that Mirror 1 moves to the exact same place that Mirror 2 was at when the pulse of light originally bounced off. When that happens, you will see a dot of light once again at the same location on the target. Since you know how fast the mirror assembly is rotating and how many mirrors are on the assembly, you can figure out the time taken by the light to travel across the room and back. Since you know the distance traveled by the light and the time taken by the light to travel, you can calculate the speed of light.

Answer 2

• Optical method: A continuos laser, pulsed by a rotating mirror or other type of device (opto acoustic, electro optical, etc.). Then the pulsed beam is divided by a beam divisor in two beams that will travel different paths, but with the same returning point, where yo have a detector (photoelectric cell or photodiode).

• Electric method: Here the light source is a led diode fed by a source pulsed with an oscilator, so we have two signals, the firsts indicates that when the led is pulsated (from the oscilator, starting signal or "trigger") and the second indicates that it is provided by the detector and mesures how long it takes for the light to cover the distance between the emisor diode and the
detector.

The first method is more mechanical, the second is purely electronic.

Those are methods you can apply nowadays in a University lab. Historically, the first to evaluate the speed of light was Roemer, based on the Jupiter satellites, measuring the retard of the eclipses when Jupiter was in its orbit point closer to Earth or in the most distant one. During nineteen century the first measurements in labs were possible with techniques based on mirrors and/or rack wheels (Fizeau, etc.)

Answer 3

When measuring speed of any moving object ,what is actually hapening is really a time measurement between two points.
If light is believed by science to be massless it cannot be considered an object. so basically non masss objects dont following standard rules of physics. Therefore if light is massless its would be immeasurable in outer space.Since we cannot obtain two absolute points.
The other sceneario would be that Light is not massless. Than there would be a scientific basis for measurement.
Nevertheless no one has been able to measure light speed at the outsckirt of the Universe.One thing that science has done is that they have measured the speed of Universal Expansion to be faster than the speed of light that was determined relative to our solar system.
Therefore on that basis all the galaxies are expanding all at once faster than the speed of light.

Answer 4

fire a laser at the moon.
measure the time it takes for the laser pulse to travel several times between earth and the moon
divide the distance the pulse travelled between the moon and earth by the time taken for the pulse

v = d/t

in metres per second.


A little difficult to do at home.

Answer 5

speed of light can be calculated by the formula-

speed=distance travelled
-----------------------
time taken