A compound lens is made of two lenses in contact having powers +12.5 D and -2.5 D. An object is placed at 15 cm from this compound lens.Find the position and nature of the image formed.

Question: A compound lens is made of two lenses in contact having powers +12.5 D and -2.5 D. An  object is placed at 15 cm from this compound lens.Find the position and nature of the image formed.

Answer: P_comp = P₁ +P₂ = + 10 D
F_comp  = 100/10 cm
1/F =1/v - 1/u
F = +10 cm, u = -15 cm, v = ?                                                             
  V= +30 cm 

Image formed will be real inverted and enlarged.