Why does condensation on a glass window make it opaque?

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In summary, the reason why fog condensed on a glass window is opaque to light is because of the water-air interface created by the tiny droplets on the glass. When light hits these droplets, it can strike at different angles, causing it to scatter and making the fog appear opaque. However, if the water is pressed into a thin sheet between two flat surfaces, it will become transparent again.
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dipole
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Fog condensed on a glass window is just a very thin layer of water droplets, so why is it so opaque to light? Normally light passes through a water-glass interface just fine, but why not in the case of condensation?
 
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dipole said:
Fog condensed on a glass window is just a very thin layer of water droplets, so why is it so opaque to light? Normally light passes through a water-glass interface just fine, but why not in the case of condensation?

It's not just the water-glass interface that's the problem, it's the water-air interface. You have lots of tiny beads of water on the glass, so incoming light will strike perpendicular to the surface of the water at one point (near the center of a droplet) yet almost parallel to it at another very close point (the edge of the droplet).

Take a second piece of glass, press it flat against the first so that water in between is pressed down into auniform thin sheet between the two surfaces, and it will go back to transparent again.
 

1. Why is a foggy window opaque?

Foggy windows appear opaque because they are covered in tiny water droplets, which scatter and diffuse light, making it difficult for light to pass through and resulting in the appearance of opaqueness.

2. What causes windows to become foggy?

Windows become foggy when there is a difference in temperature between the inside and outside of the window. This temperature difference causes water vapor from the air to condense on the surface of the window, creating tiny water droplets that fog up the window.

3. How does fog affect visibility through a window?

Fog significantly reduces visibility through a window because the tiny water droplets that make up the fog scatter and diffuse light, making it difficult for our eyes to see through the window clearly.

4. Can foggy windows be prevented?

Foggy windows can be prevented by reducing the temperature difference between the inside and outside of the window. This can be achieved by using double-paned windows, adding weather stripping to the window frame, or using a dehumidifier to reduce moisture in the air.

5. How can foggy windows be cleared?

Foggy windows can be cleared by removing the moisture from the surface of the window. This can be done by using a cloth or squeegee to wipe the window, using a hairdryer on a low heat setting, or simply waiting for the temperature inside and outside of the window to equalize and the fog to evaporate.

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