Question #631d7

1 Answer
Apr 18, 2017

#6.bar6cm#

Explanation:

When two thin convex lenses of focal length #f_1 and f_2# are placed at a distance #d# apart, the equivalent focal length #F# of the system is given by the expression

#F=(f_1cdotf_2)/(f_1+f_2-d)#

Inserting given values we get
#F=(20cdot5)/(20+5-10)#
#F=100/15=6.bar6cm#