why sound can pass through walls but light can,t
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Whether any form of wave can pass through an object depends on how strongly that wave is reflected, scattered or absorbed.
Sound waves are certainly reflected by a wall, otherwise you wouldn't hear an echo from it, but not all the sound is reflected so some travels into the wall. Whether the sound is scattered and/or absorbed in the wall depends on what the wall is made from. Remember that sound is a mechanical vibration. The sound hitting the wall makes the wall vibrate and the other side of the wall makes the air on the other side vibrate. A good solid wall won't disperse the vibrations too much, so you will get some sound through it. A wall filled with e.g. fibreglass insulation, will absorb the sound far more, so it will transmit less sound.
Light is also reflected by a wall, otherwise you wouldn't be able to see it. How much light is reflected depends on the wall: a white painted wall will reflect more of the light than a black painted one. However the dominant interaction with the wall is probably scattering. If the wall was made of glass then obviously the light would pass through it. A concrete wall is made from miniscule grains of calcium carbonate and aluminosilicates, and while these materials are transparent to visible light, reflections from all those grain boundaries scatter light strongly. If a concrete wall was very thin e.g. 0.1 mm you would still get some light transmission through it.
Sound waves are certainly reflected by a wall, otherwise you wouldn't hear an echo from it, but not all the sound is reflected so some travels into the wall. Whether the sound is scattered and/or absorbed in the wall depends on what the wall is made from. Remember that sound is a mechanical vibration. The sound hitting the wall makes the wall vibrate and the other side of the wall makes the air on the other side vibrate. A good solid wall won't disperse the vibrations too much, so you will get some sound through it. A wall filled with e.g. fibreglass insulation, will absorb the sound far more, so it will transmit less sound.
Light is also reflected by a wall, otherwise you wouldn't be able to see it. How much light is reflected depends on the wall: a white painted wall will reflect more of the light than a black painted one. However the dominant interaction with the wall is probably scattering. If the wall was made of glass then obviously the light would pass through it. A concrete wall is made from miniscule grains of calcium carbonate and aluminosilicates, and while these materials are transparent to visible light, reflections from all those grain boundaries scatter light strongly. If a concrete wall was very thin e.g. 0.1 mm you would still get some light transmission through it.
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Sound is a mechanical wave whereas light is an electromagnetic wave. A mechanical wave is propagated by the oscillations in the particles of the medium. So, sound can travel through solids, liquids, gases and plasma. Although light does not require a medium for propagation, it cannot travel through an opaque object. The light gets reflected from the surface of the opaque object.
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