Question

Data &Results of Calculations: ir hes angle POD angle PCE Length of line PH (ainches angle AOD angle BCE Length of line P'H Error Error Const. Error %Diff % Difference %Diff QUESTIONS: 1. Why is it impossible to form real images with a plane mirror? 2. Why are ordinary plane mirrors coated on the back instead of the front like astronomical mirrors. Why would such a back coating be undesirable for astronomy? 3. What error is introd uced by the thickness of the mirror? CONCLUSIONS& SOURCES OF ERROR: (Continue on back of sheet.)

Answer 1

1: Virtual Images are those images which can be seen into the mirror where as the real images are those images which can be projected on the screen.

To form a real image the ray coming from object from any point must have to converge at some point. So, if we have any object and its radiation falls on the plane mirror then its radiation can't be converged at a single point because a mirror never converges the incident ray. Below I have shown how the radiation from any finite distant object get diverged after the reflection of the plane mirror forming a virtual image.

2: The ordinary mirror which we uses in our houses or in many other commercial purposes are low precision mirrors. They have low precision because they have two reflecting surfaces, one is the front of mirror where low percentage of the light is get reflected and other is the back of mirror (which is coated by aluminum) have large reflection percentage. The formed image is the superposition of both reflected rays. But for some astronomical observations these low precision mirror will make the result of very distant object like star etc. wrong (or incorrect with low precision quality). So we avoid these kind of mirrors and uses the mirror which have coating on the front surface due to which only one kind of radiation are present in the image formation.

3: The error present in the formed image due to the thickness of mirror is termed as reflective error. It depends on the type of mirror which we are using in our observation. It also depends on which side of the mirror is coated. This is also termed as the zero thickness error.

Below is the image for problem 1 :

See, the radiation gat diverged after reflection -- Real object virtual Image. Thirror.