2007-05-10 08:05:29 · 4 answers · asked by Craig B 1 in Science & Mathematics ➔ Physics
The speed of light is not calculated. It's a measured constant. (Now it is actually defined so other physical quantities are pegged off of it).
2007-05-10 08:11:24 · answer #1 · answered by Anonymous · 0⤊ 0⤋
The constant 299,792.458 km/s is the speed of light in vacuum. However, according to Einstein's theory of General Relativity, the speed of light appears to vary with the intensity of the gravitational field.
You can estimate the speed of light using a laaser pointer as follows:
Point the laser at the object.
Now move the laser one meter to the right.
Now adjust the laser so it is pointing at
the object again.
Measure the angle you had to move the laser
through to make it point at the same place as before.
Now you know the base and two angles of a right triangle.
A little trigonometry will get you the distance.
In fact, if you have two lasers (or a beam splitter)
you can mount the two lasers on a board a meter
apart, one fixed, and one rotatable. A friend
can walk ten feet away, and after you make both
lasers point at him, you mark the amount of rotation
of the movable laser as 10 feet. Then have your friend
move to 20 feet away, make both lasers point at him,
and mark that as 20 feet. Keep doing this, and you
won't need trigonometry, you can just read off
the distance on your homemade laser rangefinder.
Another way is to use a 100 Mhz oscillator to turn
the laser on and off every 10 nanoseconds. Use a telescope
with a sensitive photodiode in the eyepiece to look
at the spot. Feed both signals (the one turning the
laser on and off, and the one from the photodiode)
into an oscilloscope, and look at the phase shift of
the two square waves. Each nanosecond is about 1
foot (30 centimeters). You could also feed both
signals into an XOR gate chip, and get a pulse-width
modulated signal out, reading 0 volts (after low pass
filtering) for 0 feet, and 5 volts for 5 feet. Using
a slower oscillator will get you longer ranges (10 Mhz
will get you 5 volts at 50 feet).
I have actually utilzed a 20 Mhz oscillator, and used it to measure the speed of light successfully.
Dr. H
2007-05-10 08:46:08 · answer #2 · answered by ? 6 · 0⤊ 1⤋
Currently, there isn't one.
The speed of light is one of the measured values that has to be input into the Standard Model in quantum mechanics. This is thought to be unsatisfactory, and physicists would like to develop a model that predicts its value.
2007-05-10 11:24:24 · answer #3 · answered by Anonymous · 0⤊ 0⤋
It is a constant and travels at 186,000 miles per second.
2007-05-10 08:12:54 · answer #4 · answered by booman17 7 · 0⤊ 0⤋