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Which can travel through a vacuum: sound or light?
A. Sound
B. Light
C. Both
D. Neither
Correct Answer Is Option = Light
Notes / Explanation
Of the two, it is light that can travel through a vacuum, while sound cannot, and this important difference between light and sound reveals a great deal about the nature of these two forms of energy. A vacuum is a space that is completely empty of matter, containing no air or any other substance, such as the vast emptiness of outer space between the stars and planets. The question of whether sound and light can travel through such a space leads to one of the fundamental distinctions between them. Sound is a form of energy that travels in the form of waves, but these waves require a material substance, known as a medium, through which to travel, because sound is produced by the vibration of particles, and the sound is passed along from one particle to the next. In the air, for example, sound travels by causing the particles of the air to vibrate and pass the vibration along, and sound can also travel through liquids and solids. However, in a vacuum, where there are no particles at all, there is nothing to carry the vibration, and so sound cannot travel through it. This is why, in the emptiness of outer space, there is complete silence, and no sound can pass from one place to another. Light, on the other hand, is a form of energy that does not require a material medium in order to travel, and it is able to pass through the empty space of a vacuum. This is why the light of the Sun and the distant stars is able to travel across the vast empty reaches of space to reach the Earth, even though there is no air or other substance in between. The ability of light to travel through a vacuum, together with the inability of sound to do so, is one of the key differences between them, and it explains many of the phenomena that are observed, such as the fact that we can see the Sun and stars but cannot hear any sound from them. The study of the differences between light and sound is an important part of the science of physics. For PPSC and other competitive examinations, the key points to remember are that light can travel through a vacuum while sound cannot, that sound requires a material medium such as air, liquid or solid to travel because it is passed along by vibrating particles, that a vacuum is a space empty of matter, and that this is why there is silence in outer space even though light from the Sun and stars reaches the Earth.
