Physics Topics can also be used to explain the behavior of complex systems, such as the stock market or the dynamics of traffic flow.
What is the Angular Magnification of an Optical Instrument?
Optical instruments which include magnifying glass, microscope, telescope, etc. are used as aids to vision for clarity and magnification.
Visual angle: When we see an object, the bigger the size of the image on the retina, the bigger is the apparent size of the object to us. The angle subtended by the object at the eye is known as the visual angle. The larger the visual angle, the larger is the size of the image. So the apparent size of the object is determined by the visual angle.
In Fig. A and B are the two different positions of an object. Suppose the visual angles subtended at the eye are θA and θB at these points. Now, according to the figure θA < θB. So the object looks smaller at A than at B. For example, cars and human beings look very small when we observe them from the roof of a high-rise building. Again if the two objects A and C of different heights subtend equal angles at the eye they will appear
of the same height. The size of the sun is much larger than that of the moon. But these two appear of same size as they subtend equal visual angles at our eyes.
As the object approaches the eye, the visual angle increases. So the apparent size of the object also increases. When the object is placed at the near point the apparent size becomes as great as possible. If the object is nearer to the eye than its near point, the impression on the retina is large but indistinct. So, there is a limit to the distance to which an object can be brought near to the eye. An instrument just removes these shortcomings.
Angular magnification or magnifying power: The magnifying power of a visual instrument is the ratio of the angle subtended at the eye by the image to the angle subtended at eye by the object. This magnifying power of a visual instrument is called angular magnification.
∴ Angular magnification
= \(\frac{\text { angle subtended at eye by the image }}{\text { angle subtended at eye by the object }}\)
It is to be noted that there is a difference between linear magni-fication (vide the chapter on lens) and the so called angular magnification in case of visual instruments. Linear magnifica-tion is unnecessary in visual instruments. Because in these instruments instead of the real size of the image its apparent size is considered e.g., in telescope the size of the image of a distant object is much smaller than the real size of the object. In spite of that the image looks large enough because its visual angle is generally large.