A lens of focal length 5 cm is being used by Debashree in the laboratory as a magnifying glass. Her least distance of distinct vision is 25 cm.
- What is the magnification obtained by using the glass?
- She keeps a book at a distance 10 cm from her eyes and tries to read. She is unable to read. What is the reason for this?
Answer:
- Focal length of given lens, f = +5cm (given)
- The person’s least distance of distinct vision is 25cm .
- This means the image will be formed at 25cm from the lens.
- Since she does not require a screen to view this object, it is a virtual image and is formed on the same side as the object .
- Thus, v=-25cm
- Magnification, m = v/u
