Give reasons:
A simple microscope is used by watch repairers.

Hint:A simple microscope is used to magnify objects close to it. The microscope uses a convex lens and the object is less than one focal length from the lens, which results in a magnified image.

Complete step by step answer:
A microscope is a device that uses two convex lenses with relatively short focal lengths to magnify small, close objects. A microscope has an objective lens and an eyepiece lens. The object to be viewed is placed on a transparent slide and is illuminated from below. The light passes by or through the object on the slide and then travels through the objective lens. The objective lens is a convex lens. It forms a real, enlarged image of the object because the distance from the object to the lens is between one and two focal lengths. The real image is then magnified again by the eyepiece lens (another convex lens) to create a virtual, enlarged image. The final image can be hundreds of times larger than the actual object, depending upon the focal lengths of the two lenses. The total magnification is the magnification of the objective times the magnification of the eyepiece.
Additional information:
The magnification of a simple microscope is given by,
\[M=1+\dfrac{D}{F}\]
Where, D = least distance of the clear vision.
F = focal length of the convex lens.

Note:A magnifying glass also uses a convex lens and the lens is adjusted so that the object is less than one focal length from the lens. This also gives us a magnified image.