How to use a plane mirror to eliminate the parallax error associated with a measurement.

Question

aabomosalam1998 · Answer

If I wanted to measure the height of object A given only a meter rule and a plane mirror. How can I trust the measurements I have made while conducting the experiment. .

osprey · Answer

Parallax error. I remember this as reading a value off a needle and scale. The needle points to a certain place, say 5, on the scale. Well, does it ? If your eye is directly in line with the needle and the scale (sort of at right angles to the scale), then yes. However, the needle and the scale are SEPARATED by a distance - small, but there. So, if you looked at the needle and scale obliquely - from an angle - then you'd get a slightly different reading. What a mirror does here is to allow you to make sure that the needle, the scale, and your eye are all in the same line and that line is at right angles to the scale. So, you get a true reading. I'd risk a diagram, but I don't like the graphics on this site so that'll have to do for the moment. http://perendis.webs.com