18. A. The focal length of a lens is dependent on the: B. radius of curvature of the lens. C. refractive index of the material the lens is made from. D. shape of the lens and its refractive index. location of the object used. Use the following information to answer the next question. iv. 19. The systems that would produce a virtual image are: A. i and ii. B. i and iv. C. ii and iv. D. iii and iv. 20. The kinetic energy of photoelectrons is graphed as a function of frequency of incident light. Select the properly matched quantities. y-intercept x-intercept slope A. Planck's constant work function threshold frequency B work function Planck's constant threshold frequency work function Planck's constant C. threshold frequency work function threshold frequency Planck's constant D