Which quantity in the equation Emc2 represents speed of light?

Answer 1

The speed of light is 299,792,458 meters per second - in a vacuum or 186,282 miles per second in a vacuum. And according to the theories of motion - nothing can travel faster than the speed of light. If it does - it bends time and time will slow down and eventually - as the speed increases - time will start going backward - and you will travel back in time!!! And of course this is theory - it has never been tested - as the fastest movement - relative the the person measuring the movement) has never even approached 50% (93,000 miles per hour) of the speed of light!

The speed of light - as all speeds are measured - is determined by the distance traveled - divided by the amount of time it took to travel that distance. A race car, for example, measures it's speed by the amount of time to travel a specific known distance (quarter mile - or 500 miles) divided by the time it took to travel that distance.

The speed of light is something we've figured out only in the last 100 years, right? Well, once more, our forebears surprise us. It turns out we've known the speed of light since before the birth of Johann Sebastian Bach.

That knowledge came close on the heels of the invention of the first telescopes in the early 1600s. In 1644, Ole Roemer was born in Jutland, Denmark. He took up the new study of astronomy with the early greats of that field.

By 1675 Roemer was 31 and working in Paris with Picard. He was interested in the movement of Jupiter's nearest moon. He tracked it as it orbited in and out of Jupiter's shadow. It entered the shadow, then reemerged exactly 42 hours, 28 minutes, and 35 seconds later. It moved with constant and exact regularity.

So Roemer measured 100 cycles and found that in one hundred cycles, Jupiter's moon could be relied upon to emerge EVERY TIME - right on schedule - to the exact second!! So he measured different lengths of time!! One was six months -- 100 laps -- and it was then that Roemer set his clocks and focused his telescope on Jupiter in the winter. In the spring - he waited and waited - but no moon appeared!! Finally it danced out of the shadows a full 15 minutes late. But why was the moon late - there must be a reason!

After much discussion, Roemer concluded that the moon was still appearing at the same time - and it was the earth that had moved!! The earth had swung hundreds of millions of miles away from Jupiter during the long winter months so light had to travel that vast distance to see Jupiter's moon!!! It had obviously taken the extra time to do so. (Also discovering that earths orbit around the sun is egg-shaped - NOT a circle)!

He put pencil to paper and concluded that light had to move 192,500 miles per second to lose just those fifteen minutes. Not bad at all! Roemer was within three percent of the right value (186,282 miles per second). And that was less than 70 years after we first had telescopes.

Just to be sure, Roemer calculated when we'd get that 15 minutes back, as the earth moved back toward Jupiter and spring began. He was right again.

Today the speed of light is measured - and found to be accurate - by pointing a laser to one of the many groups of mirrors and reflectors that were set up on the moon by the 1970's moon landing missions. Now computers accurately measure the speed light with a laser - and can determine the exact speed of light to within 1/quadtrillionth of a second! These mirrors also measure the movement of earthquakes on the earth - from the moon - to within 1/10,000,000,000th of an inch!

Answer 2

The speed of light in a vacuum is equal to the reciprocal of the square root of the product of the electric constant and magnetic constant. That is 1/sqrt(E*M) where E is the electric constant and M is the magnetic constant. To find the speed of light traveling through a substance is more complex, but can be found using experimentally known values called the 'refractive index' of the substance. The refractive index of a substance is equal to the speed of light in a vacuum divided by the speed of light in the substance.

Answer 3

c represents the speed of light - in metres per second.

Answer 4

C