Q.
Which of the following form(s) a virtual and erect image for
all positions of the object ?
IIT JEEIIT JEE 1996
Solution:
For a lens $ \frac{1}{v}-\frac{1}{u}=\frac{1}{f} \, \, \, i.e. \frac{1}{v}=\frac{1}{f}+\frac{1}{u}$
For a concave lens,/and u are negative, i.e. v will always be
negative and image will always be virtual.
For a mirror:
$ \, \, \, \, \, \, \, \frac{1}{v}+\frac{1}{u}=\frac{1}{f} \, \, \, i.e. \frac{1}{v}=\frac{1}{f}-\frac{1}{u}$
Here, / is positive and u is negative for a convex mirror.
Therefore, v is always positive and image is always virtual.
