light question?

Question

say there is a metal tube,when you put a lid on the cylinder why does it get dark why isn't the light still bouncing around in the tube?

Answer 1

I'm imagining that you're looking into a tube with the other end initially open, and then closing the other side.

Initially, you can see light in the tube because photons are continuously streaming out from light sources, into the tube, and bouncing down towards your eye, all at the speed of light. You can observe this light because the photons are falling on your retina and being absorbed and recorded.

When the light source is shut off, the photons currently within the tube -do indeed continue to bounce about the tube-, however, they will all quickly reach the end of thier journey, either absorbed as heat by the tube, or by your retina.

Imagine a cop looking for speeding cars on a stretch of highway. There is a traffic accident a few miles up the road, blocking all traffic. For several minutes, though, the officer will continue to observe the cars passing by him. After he has observed all the cars that got through before the accident, there will be no more cars observed until the accident is cleared away. If the cars were moving at the speed of light, the traffic would appear to drop to nothing (in this analogy, darkness) almost immediatley.

This is analogous to what you're seeing, but the difference is that the photons (usually) don't somehow escape, theier energy is absorbed over many, many collisions and reflections.

Answer 2

The metal is not a perfect mirror, at each bounce some of the light gets adsorbed

Answer 3

point a flashlight into the tube, you will be able to see then!