Question

a.) How is the image formed in hollow and bulged mirrors?
b.) Explain the difference between real and virtual images.
c.) Derive the mirror equation.

Answer 1

ANSWERS

a) I assume that hollow and bulged mirrors refer to the concave and convex mirrors. There is no harm in this assumption as a concave mirror consists of a reflecting surface curved inwards, i.e., hollow like bowl and a convex mirror consists of a reflecting surface curved outwards, i.e., bulged like the backside of a spoon.

Now let us undertand the image formation in these mirrors. First let us consider a concave mirror.

As usual we will be encountering this with ray diagrams. Before going for the ray diagrams let's try to keep in mind one important point which is mentioned below,

Light always follows the law of reflection, i.e., angle of incidence (i) = angle of reflection (r), whether the reflection occurs off a curved surface or off a flat surface. In order to determine the direction in which an incident light ray would reflect, we have to determine the normal to the surface at the point of incidence. For a concave mirror, the normal at the point of incidence on the mirror surface is a line that extends through the center of curvature (this applies for a convex mirror as well). Once the normal is drawn the angle of incidence can be measured and the reflected ray can be drawn with the same angle.

So always keep this point in mind while drawing ray diagrams. This will help you in getting accurate image locations.

One more rule you have to follow is, from the object draw 2 incident rays and the corresponding reflected rays. The point where the reflected rays intersect is the point of image formation.

Ray diagrams for both concave and convex mirrors are shown below.

                                                                                                        Fig 1: Concave Mirror

                                                                                                                      Fig 2: Convex Mirror

b) One main difference between Virtual Image and Real Image is that a real image can be formed on a surface, such as a card or a movie screen whereas a virtual image cannot be formed on a surface, it truly exists only within the brain but nevertheless is said to exist at the perceived location. So the existence of a virtual image depends on whether you are seeing or not but the existence of a real image does not depend on your seeing it and is present even if you are not seeing it.

This difference can be understood even better if you look through the ray diagrams above.

c) The answer is in the images below.

c)