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 Question:
We can SEE the light, is it a substance?
Answer:
No! Unlike wood,
iron, air, and sand,
light isn't a substance. Light has no mass, and no volume, either. Usually, we see
it as a kind of energy. This energy is similar to kinetic energy, thermal energy, and
nuclear energy. Nowadays, solar energy gradually replaces petroleum,
because solar energy is clean and cannot be used up.
Question:
Does the light have special
characteristics?
Answer:
Exactly, light is marvelous. It can go forward without any
medium. For example, the sun is one of light sources; most of light in earth
comes
from the sun. Although the universe is nearly vacuum, light can reach the earth
without problem. In physical field, we call this radiation.
Question:
How fast is the light?
Answer:
The velocity of light is
surprisingly high. That's why lightning always comes before thunder. In a second,
light runs about 300,000 kilometers far.
And, up to now, it's the highest speed we know. From sun to earth, it takes about 500
seconds for light. If we were able to run so fast, we would travel between
stars. However, according to Einstein's theory, there's no matter can run as fast
as light, even though it has a powerful propeller.
Question:
How to measure the speed of
light?
Answer:
Light goes too fast, we can't measure it's speed by simple method, but
scientists can use some indirect ways such as Fizeau toothed wheel. It was
the earliest way to measure the speed of light in earth.
PS: light year:
a kind of distance units
the distance light can run in a year
Fizeau toothed wheel
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