(a) (i) Draw a ray diagram to show the image formation by a compound microscope. Obtain the expression for the total magnification of the microscope when the final image is formed at infinity. (ii) In a compound microscope, an object is placed at a distance of $1.5\text{ cm}$ from the objective of focal length $1.25\text{ cm}$. The eyepiece has a focal length of $5\text{ cm}$. The final image is formed at infinity. Calculate the distance between the objective and the eyepiece. OR (b) (i) Using Huygens' principle, explain the refraction of a plane wavefront, propagating in air, at a plane interface between air and glass. Hence verify Snell's law. (ii) Use mirror formula to deduce that a convex mirror always produces a virtual image of an object kept in front of it.