An object placed 40 cm in front of a thin convex lens is moved to 60 cm from the lens. If the focal length of the lens is 30 cm the ratio of magnification of the image at the initial position to the final position is:

An object is placed 25 cm in front of a fully silvered concave mirror of focal length 15 cm . A plane mirror is placed 35 cm behind the concave mirror on the side opposite to the object. The final image after reflection first from the concave mirror and then from the plane mirror is formed at:

A glass slab of 16 cm thickness has its bottom surface silvered. An air bubble is located inside the glass slab at a distance of 8 cm from the top surface. The refractive index of glass is 1.6 . Which of the following correctly represents the number of images seen by an observer looking vertically downwards from air onto the top surface?

A. Only one image is seen at a depth of 5 cm

B. Multiple images are formed due to multiple reflections and refractions

C. Only one image is seen at a depth of 16 cm

D. Two images are seen at depths 5 cm and 15 cm

An object is placed at an unknown distance from a convex objective lens of focal length 5 cm . The objective lens forms a real image which acts as an object for a convex eyepiece of focal length 6.25 cm . The distance between the objective and eyepiece is 20 cm . The microscope is adjusted so that the final image is formed at the least distance of distinct vision $(25 \mathrm{~cm})$. Which of the following is correct?

A. Object distance $=7.5 \mathrm{~cm}$; Total magnification $=10$

B. Object distance = 10 cm ; Total magnification = 20

C. Object distance $=5 \mathrm{~cm}$; Total magnification $=20$

D. Object distance = 2.5 cm ; Total magnification = 10