An object is placed at a distance of 10 cm from a co-axial combination of two lenses A and B in contact. The combination forms a real image three times the size of the object. If lens B is concave with a focal length of 30 cm, the nature and focal length of lens A is__________
A. convex, 12 cm
B. concave, 12 cm
C. convex, 6 cm
D. convex, 18 cm
Answer:C
An object is placed at a distance of 10 cm from a co-axial combination of two lenses A and B in contact. The combination forms a real image three times the size of the object. If lens B is concave with a focal length of 30 cm, the nature and focal length of lens A is__________
A. convex, 12 cm B. concave, 12 cm C. convex, 6 cm D. convex, 18 cm