Question

a beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12cm from P. At what point does the beam converge if the lens is (a) a convex lens of focal length 20cm,and (b) a concave lens of focal length 16cm.​

Answer 1

Answer:

Answer

(a). According to the given case, object is virtual, u=+12 cm

The focal length of the convex lens is f=+20 cm.

Using lens equation,

v

1

−

u

1

=

f

1

v

1

−

12

1

=

20

1

v=7.5 cm

(b). Now the focal length of the concave lens, f=−16 cm

v

1

−

u

1

=

f

1

v

1

−

12

1

=

−16

1

v=48 cm