I was just doing this thought experiment: Consider a well illuminated cubical room with all its inner six faces as mirrors. Now we place an insect inside the cube and it starts moving on the floor of the room with uniform velocity making an angle with the mirrors( for e.g maybe along the diagonal of the floor). Assume that room is big enough and insect doesn't change its direction or anything like that. If we only consider the images in the mirrors formed by first reflection only i.e. the image when light directly from the object strikes the mirror. What will be the speed of these images in the plane mirrors?

Now what I think is that it should be same as the speed of the insect as the image in plane mirror also shows us the depth(Distance of an object from the mirror is equal to to distance of image inside the mirror. Plane mirror property). What I mean to say is that image formed is not a projection of object on the mirror.

I just want to know your opinion to check whether my logic is correct.


1 Answer 1


You are right that the image formed is not a projection of the object on the mirror; it is a virtual image on the other side of the mirror surface where a line connecting the two images is perpendicular to the mirror and the mirror is on the midpoint of the line. The velocity of an object is the same as the velocity of its image except that the component of the velocity vector parallel to the line is reversed.


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