Question

Which of the following converge a light beam the most?
a. A convex lens of focal length 0.5m
b. A convex lens of fical length 0.75
C. A concave lens of focal length 0.75
d. A concave lens of focal length 1m​

Answer 1

Answer:

Power of the combination of lens P=

f

1

1

+

f

2

1

−

f

1

f

2

d

Given : f

1

=1 m, f

2

=−0.25 m and d=0.75 m

So, P=

1

1

+

−0.25

1

−

(1)(−0.25)

0.75

P=1−4+3=−3+3=0

Thus the above combination acts as plane surface and so, the emerging beam is parallel to the principal axis.