how does one calculate the speed of light?

Question

use illustrations in your answers please

Answer 1

Well, this will probably go right past you, but the calculation is very simple. You take Maxwell's equations in vacuum - http://en.wikipedia.org/wiki/Maxwell's_equations#In_vacuum.2C_without_charges_or_currents. You then take a curl from, say, the third one. curl of a curl gives you a Laplace operator - that is second derivative in space. You then substitute the fourth equation into what you've got and get a second derivative in time. Now - second derivatives in time and space mean that you've got a differential equation, which describes a wave. The term 1/sqrt(mu0*epsilon0), as follows from general properties of such equations is equal to the velocity of the wave. Voila.

Answer 2

If you fancy meauring the speed of light yourself, there is a fun experiment you can do with a microwave oven - see link below. I've also heard of it being done with marshmallows, although my personal favourite is a (raw) poppadom.

In summary, you disable the turntable, and then heat up the food of your choice. The food will cook more in some places than others due to standing waves in the microwave (and with a poppadom, you literally get peaks!). The distance between peaks is half the wavelength. The microwave oven should have the frequency written on a plate somewhere, so you can calculate the speed of light.

Answer 3

Originally it was thought that light transmitted instantaneously. Then astronomers noticed that other objects in the solar system were not exactly where they should be, depending on how far away the Earth was from them (because the Earth is moving in space, too). If you know how far away the other object (planet, moon, whatever) is, then you can work out the speed of light from the slightly incorrect locations alone.

Otherwise, there are dozens of ways on Earth to figure out the speed of light. Most of these involve fairly sophisticated instruments, like mirrors, rotating blades and (ideally) an air vaccuum. You'll need such equipment and some expertise if you want to measure the speed of light precisely. But you can also measure it within 5% of the true value doing a fun home experiment, metling marshmallows in your kitchen microwave (AND you get to eat the marshmallows when it's all done!).

Answer 4

Basically they have a long(miles) tube which they know the length of, they send a light pulse along it.A sensor at the other end works out the time the light has taken to make the journey.
Speed is calculated from the formula..

Speed = Distance/Time.

Answer 5

there are basically three methods used to calculate speed of light.
1. Fizeau method(16th century)
2. Focault rotating mirror method(17,18 century)
3. Michelson's octagonal mirror method.(used last 2 centuries)(though last 2 are used frequently)

all three of them use certain principles of light to measure its speed.
1. Fizeau method uses a long tube along which light travels and gets reflected from the other end and the time taken to travel the distance is calculated and then the speed is found.(originally the distance used was 6.92km odd)
2. Focault uses a rotating mirror to find the reflection of a source of light and its frequency isused tofind the speed oflight.
an indepth discussion is found here
http://courses.washington.edu/phys331/speed_of_light.pdf
3. Michelson also uses almost the same principle but he uses an octagonal mirror.

an entire history is here
www.phys.ufl.edu/~avery/course/3400/f2001/lectures/velocitylight.pdf

Answer 6

James Clerk Maxwell calculated the speed of light as 1/sqrt(ε0·μ0), where ε0 and μ0 are the permittivity and permeability of free space respectively. Basically, he showed that a moving electric field in space would induce a moving magnetic field and vice-versa, and the whole thing would radiate away from its origin at the speed we now know as c.

Answer 7

All great answers but why calculate it, its a given constant. Why make things more difficult for yourself.

3 x 10^8 m/s

Answer 8

By using a light sensitive probe.

Answer 9

By using the index of refeaction of the medium (n)
n = c/v

c: the speed of light in vaccum
v: the speed of light in that medium

Answer 10

Try this

http://en.wikipedia.org/wiki/Speed_of_
light#Measurement_of_the_speed_of_light

a thumbs down???? how can the right answer be a thumbs down.... more village idiots on yahoo again?