Glass is clear because the electrons in its atoms don't absorb the photons of visible light, allowing the light to pass through.
Here's a more detailed explanation:
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The Composition of Glass: Most common glass is made primarily of silica (silicon dioxide). The arrangement of atoms in glass is amorphous, meaning it lacks the long-range order found in crystals.
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Electrons and Energy Levels: Atoms have electrons that exist in specific energy levels. Electrons can absorb a photon (a particle of light) if the photon's energy matches the precise energy difference between two electron energy levels. When an electron absorbs a photon, it jumps to a higher energy level.
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Why Glass Doesn't Absorb Visible Light: The energy carried by photons of visible light does not match the energy gaps between electron energy levels in silica molecules. This means that when visible light strikes the glass, the electrons in the glass atoms cannot absorb the energy.
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Light Passes Through: Since the electrons don't absorb the light, the photons of visible light simply pass through the glass. This transmission of light is what makes glass appear transparent.
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Impurities Can Change Things: Impurities in the glass can change the energy levels of the electrons, causing absorption of some wavelengths of light. This is how colored glass is created. For example, adding iron oxide can make glass appear green, as the iron absorbs some wavelengths of light.
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Reflection and Refraction: While most of the light passes straight through, a small portion is reflected at the surface of the glass and some is refracted (bent) as it enters and exits the glass. This is due to the change in the speed of light as it moves from air into glass and back into air. However, these effects don't significantly affect the overall transparency.
In summary, the transparency of glass arises from the fact that the energy of visible light photons is not the right "size" to be absorbed by the electrons in the silicon dioxide molecules that make up the glass. The electrons effectively ignore the light, allowing it to pass through.
