Hi, I'm Steve Jones and I'm going to tell
you how fast light travels. Well, light itself
is a form of electro-magnetic radiation. Now,
electro-magnetic radiation, it, comes in many
forms. And starting at one end, we have radio
and then we have we have microwaves. And next
to microwaves we have infrared and then we
have visible radiation which we call light.
And then we have ultraviolet and onto x-rays
at this end. So we have many types of electro-magnetic
radiation and the similarity between them
is the speed. The speed of electro-magnetic
radiation is always 3 X 10 8 m/s or 186,000
miles/sec or 300,000 km/sec in vacuo; in vacuo.
That means in a vacuum. Of course if I actually
ask light to travel through something like
glass; glass is a good example; it would go
down to 200,000 km/sec because it travels
slower in transparent media. So if it's in
plastic, it would be about 250,00; in glass,
200,000 and so on. So the speed of light depends
not just on what type of radiation it is,
because all of the radiation have the same
speed; all of these radiations. It depends
also, on what it is traveling in. But in vacuo,
the answer of those three, take your choice.
