# Circles of light

1. Jan 31, 2008

### John Richard

Hello to whoever is kind enough to read this!

A question,

Suppose I place a rotating laser at the centre a circle so that the beam will hit the inner face of the circles circumference.

If the radius of the circle is one light second, then the circumference would be 2pi light seconds. (We can ignore the length of the laser source device)

If I now rotate the laser through 360 degrees in one second.

What will I see on the circles inner circumference?

2. Jan 31, 2008

### Loren Booda

A projection of the laser sweeping across the circumference with 1/(2pi) original intensity?

3. Feb 1, 2008

### Troels

I think the correct term is "What will you *observe*?" - there is a difference. But that depends on the point of view... If you observe from rest, #1 has given the aswer. But if you observe from a frame that is rotating with the laser, the problem is more subtle, since then you are not in a inertial frame!

Last edited: Feb 1, 2008
4. Feb 1, 2008

### John Richard

That depends on the point of view!

Lets assume as the viewer you are within touching distance of the circles inner circumference