Question

Define the magnifying power of a microscope in terms of visual angle.

Answer 1

The rays after refraction form a convex lens converge. This convergence results in the formation of a real image. The image is real, inverted and magnified only when the object is placed between the focus and the center of curvature on one side. A microscope makes use of a biconvex lens.

Complete step by step answer: Let us first see what magnification is. Magnification, as the word suggests, can be defined as the action of magnifying. It refers to the process of enlarging an object with the help of a lens. The actual size of the image is the same, only the size of the image is increased. Magnification is of many types. The two basic types of magnification are: Linear magnification: It refers to the ratio of image length to object length. Angular magnification: It refers to the ratio of the tangents of the angles subtended by an object and its image from a given point. For a microscope, the magnification can be defined as the ratio of the angle subtended by the image on the eye to the angle subtended by the object on the eye when the object is at least distance of distinct vision.

The linear magnification of the microscope can be given by,
${m_l} = \dfrac{u}{v}$
Here $v$ is the distance of the image, $u$ is the distance of the object and ${m_l}$ is the magnification of the linear magnification.
The angular magnification of the microscope can be given by,
${m_a} = \left( {1 + \dfrac{D}{f}} \right)$
Here $D$ is the least distance of distinct vision, $f$ is the focal length of the lens and ${m_a}$ is the angular magnification.

Note: Magnification can be different depending on the number of lenses used. For example, in a microscope, a simple lens (one lens) is used whereas, in a telescope, a compound lens ( two or more) is used. A microscope makes small objects appear larger, while telescopic makes distant objects appear closer.