[" Two lenses of focal lengths "-20cm" and "+10cm" are put in combination,"],[" find the power of the combination: "]

Two lenses of focal lengths -20cm and +10cm are put in contact. Find power of the combination (A) -1D (B) -2D (C) +5D (D) +2D

Two lenses of focal length 10 cm and -20 cm are placed in contact .What is the total power of the combination?

Two lenses of focal lengths -20cm and +10cm are put in contact.Find power of the combination

Two thin lenses of focal lengths 20cm and 25cm are placed in contact. The effective power of the combination is

Two thin lenses of focal lengths 20 cm and 25 cm are placed in contact. The effective power of the combinations is

Two thin lenses of focal lengths 20 cm and 25 cm are placed in a contact. The effective power of the combination is

Two thin lenses of focal lengths 20 cm and 25 cm are placed in a contact. The effective power of the combination is

Two thin lenses of focal lengths 20 cm and 25 cm are placed in a contact. The effective power of the combination is