Lenses in ContactEasyQuestion 20230
Question
Two thin lenses of focal lengths f₁ and f₂ placed in contact. Equivalent focal length is:
- Af₁ + f₂
- Bf₁ × f₂/(f₁+f₂)Correct
- Cf₁ + f₂/2
- D1/(f₁×f₂)
Correct answer
f₁ × f₂/(f₁+f₂)
Explanation
1/f = 1/f₁ + 1/f₂ → f = f₁f₂/(f₁+f₂). Power adds: P = P₁ + P₂. Used to find equivalent lens of a lens system.