Three lenses having power 2, 2.5 and 1.7 D are kept touching in a row. What is the total power of the lens combination?

Doctor has prescribed a lens having power +1.5D. What will be the focal length of the lens? What is the type of the lens and what must be the defect of vision?

Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. What is the total capacitance of the combination.

Two lenses of power +12 and -2 dioptres are placed in contact. The combined focal length of the combination will be

If a convex lens of focal length 20 cm and a concave lens of focal length 30 cm are kept in contact with each other . (i) What will be the focal length of the combination ? (ii) What will be the power of the combination ? (iii) What will be the behaviour of the combination ?

Two convex lenses of focal length f_1 and f_2 are mounted coaxially separated by a distance. If the power of the combination is zero, the distance between the lenses is