If two lenses with focal lengths 10 cm and – 20 cm respectively are kept in contact with each other, what will be the effective power of the combination of the lenses?

If two lenses with focal lengths 10 cm and – 20 cm respectively are

1.	If two lenses with focal lengths 10 cm and – 20 cm respectively are kept in contact with each other, what will be the effective power of the combination of the lenses?
Answer» The effective power of the combination of the lenses will be + 5 D.