    Question

# A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. Which of the following is/are correct regarding the combination of these lens.

A
Power of combination of lens is 12.5 D
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
Power of combination of lens is -2.5 D
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
C
Focal length of the combination of lens is 8 cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
Focal length of the combination of lens is -40 cm
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
Open in App
Solution

## The correct options are B Power of combination of lens is -2.5 D D Focal length of the combination of lens is -40 cmLet P represents power of lens and f represents focal length of lens. Given: Power of convex lens, P1=5 D Power of concave lens, P2=−7.5 D (power of concave lens is taken as negative) So power of combination of lens = Ptotal Ptotal = P1 + P2 = +5 + (-7.5) Ptotal = -2.5 D Since we know that P = 1f (in metre) ⇒f=1P=1−2.5=−0.4 m=−40 cm  Suggest Corrections  8      Similar questions  Related Videos   Lens Formula Tackle
PHYSICS
Watch in App  Explore more