Final answer:
An objective lens, typically a convex lens, has a magnification of 40×. In a microscope, the objective lens is responsible for initially magnifying the sample and forming an image that the eyepiece can further magnify. Option A is correct.
Step-by-step explanation:
The lens that has a magnification of 40× is typically referred to as an objective lens in the context of microscopes. An objective lens is a crucial component of the microscope that collects light from the sample and forms an image. In many microscopes, objective lenses come in different magnifications such as 4x, 10x, 40x, and 100x, each providing different levels of detail.
A convex lens is often used as an objective because of its ability to converge light and form a real, inverted image at (or just within) the focal plane of the eyepiece.
This real image then serves as the object for a secondary lens, known as the eyepiece or ocular lens, which further magnifies the image. When a 40× objective lens is paired with a 10x ocular lens, the total magnification produced would be 400x.
Convex lenses can also be used as magnifiers or simple magnifiers. When an object is positioned within the focal length of a convex lens, it produces an upright, virtual, and enlarged image, making the convex lens suitable for magnifying small objects.
Convex lenses are also used as magnifying glasses, due to their ability to create enlarged virtual images when objects are placed closer than their focal length.