You have two lenses A and B of focal lengths + 10 cm and – 10 cm respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer.

Question

Philoid · Accepted Answer

Given,

Object distance u= 8 cm

Focal length of A = 10 cm

=

= 0.10 m

Focal length of B = -10 cm

=

= -0.10 m

We know,

Power of lens A = 10 Dioptres.

Since the power of lens A is positive so it is a convex lens.

Similarly,

Power of lens B= -10 Dioptres.

Since the power of lens b is negative so it is a concave lens.

We know that lens formula is:

Substituting the values of lens A in formula

Substituting the values of lens B in above lens formula:

Thus, lens A which is convex will form a virtual and magnified image of an object placed 8 cm from the lens i.e. between focus and pole of lens.