# Light and mirror question

1. May 18, 2006

### nophun6

I have a question dealing with light and a mirror.
q: A dressing mirror on a closet door is 2.0 m tall. The bottom is 0.5 m above the floor. A bare light bulb is attached to the ceiling, which is 3.0 m above the floor. The light bulb is 1 m from the closet door. The light from the bulb shines evenly in all directions into the room, illuminating the walls and floor. Some light shines on the mirror and is reflected. This reflected light also
illuminates the floor making a brighter streak of light across the floor. (a) Draw a diagram to show what happens to the light that is reflected from the mirror. (b) Put dimensions on your diagram to show the position and length of the bright streak of light

I started this question out by drawing a diagram but am really at a loss for how to draw the diagram. Any help would be appreciated.

2. May 18, 2006

### Staff: Mentor

Here's a trick for quickly understanding the behavior of reflections in a plane mirror: On one side of the mirror is the real world; on the other side is a virtual world, which is the mirror image (duh!) of that real world. The mirror world is behind the mirror the exact distance that the real world is in front of the mirror. (I hope this makes sense.) So, if a real lightbulb is shining in the room, there's also a virtual lightbulb shining (or appearing to shine) from inside the mirror. The trick is to realize that the mirror acts as a window into the virtual world behind the mirror. Think of that light as coming through the mirror as if the mirror were a window.

To actually draw the light, apply the law of reflection at the mirror surface. (Look it up if you have to.)