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Speed of Light |
Even though many others before Einstein had utilized the Principle of
Relativity in their search for scientific truth, Einstein was the first to
apply the principle to the properties of light. Prior to Einstein, scientists
thought there was a preferred reference frame for light and all other
electromagnetic radiation. But the failure of scientists to identify such a
reference frame experimentally suggested that no such frame existed.
But if there is no preferred reference frame for light, what determines its speed. Since light is emitted from a source, passes through a medium, and eventually is absorbed by an observer, it seems that one or the other of these three reference frames must pertain to speed of light. But which?
Is light a particle like a bullet, emitted with a particular muzzle velocity relative to the gun? Is it a wave, traveling with a certain wave velocity through a medium as suggested by Maxwell's Electromagnetic wave equations? Or is it like nothing else in the universe, something whose current speed is mysteriously determined by the motion of some future observer? Only experimentation could answer these question.
Observations of double stars demonstrated that the speed of light was independent of the source. Light was not like a bullet, traveling with different speeds from guns traveling with different speeds.
The Michelson-Morley experiment demonstrated that the speed of light was independent of any medium through which the earth traveled. The earth was always found to be at rest with respect to the ether (the hypothesized medium through which light traveled).
And stellar aberration experiments demonstrated that the ether was not drug along with the earth. The ether was not a fluid-like substance traveling with different speeds near different objects in space.
So the only alternative remaining is that the speed of light is determined by the observer.
However, this does not mean that the speed of light is determined by some
futuristic event when the light ray is eventually absorbed by the observer's
instrumentation. It means that the speed of light has the same universally
constant value of c = 299,792,458 m/s relative to all observers in all
reference frames. Therefore, the light ray leaves its source with a muzzle
velocity of c relative to the source, travels through space with a speed c
relative to any reference frame located in space, and strikes the observer with
a speed c relative to the absorber. Light is truly unique, it has the same
speed relative to all inertial reference frames.
Q1. Which of the following is
true? (A) Light is a particle like a bullet, emitted with a particular muzzle
velocity relative to the gun that emits it. (B) Light is a wave, traveling with
a certain wave velocity through a medium as suggested by Maxwell's
Electromagnetic wave equations. (C) Light is like nothing else in the universe,
something whose current speed is mysteriously determined by the motion of some
future observer. (D) More than one of these. (E) None of these.
Q2. Which are true? (A) A light
ray leaves its source with a muzzle velocity of c relative to the source. (B) A
light ray travels through space with a speed c relative to any inertial
reference frame located in space. (C) A light ray strikes the observer with a
speed c relative to the absorber. (D) Two of these. (E) Three of these.
Q3. Experimental observation of
which of the following demonstrated that the ether was not drug along with the
earth. (A) Double Stars. (B) Michelson-Morley. (C) Stellar Aberation. (D) More
than one of these. (E) None of these.
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