Calculate the magnifying power of a lens of power +20d when the image of an object is formed by the lens at least distance of distinct vision
Answers
microscope is a device used to see small object much magnified at the least distance of distinct vision.
Least distance of distinct vision : The minimum distance from the eye at which the objects are clearly visible is called the least distance of distinct vision. It is denoted by D. For a normal eye it is about 25 cm.
The two types of microscopes are discussed below :
1. Simple microscope or magnifying glass,
2. Compound microscope
1. Simple microscope or Magnifying glass
The size of an object depends upon the angle subtended by the object at the eye. The angle subtended depends upon the dimensions of the object and its distance from the eye. If the object is brought nearer, the angle subtended at the eye increases and the object appears bigger and more distinct. Thus to see san object distinctly, it should be moved very near to the eye. But if it is brought near the eye at a distance less than the least distance of distinct vision, it becomes indistinct. Thus to see the object distinctly, It should be moved very close to the eye but its image should be formed at the least distance of distinct vision.
An ordinary convex lens of small focal length kept close to the eye can be used as a simple microscope or magnifying glass.
hope it will help u
Answer:
power = 1/focal length so focal length = 1/20
image distance at least is 1/25
we know 1/f=1/v-1/u so 1/f+1/u= 1/v
1/20+1/25 = 9/25 so u =25/9