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प्रश्न
The focal length of a convex lens is 25 cm. At what distance from the optical centre of the lens an object be placed to obtain a virtual image of twice the size?
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उत्तर
Focal length, f = +25 cm
Image is virtual and magnified, m = +2
For a lens, magnification is
m = `v/u`
∴ + 2 = `v/u`
∴ v = 2u
Lens formula is,
`1/v = 1/u = 1/f`
∴ `1/(2u) - 1/u = 1/25`
∴ `-1/(2u) = 1/25`
∴ 2u = −25 cm
∴ u = `-25/2`
∴ u = −12.5 cm
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संबंधित प्रश्न
A lens forms an erect, magnified, and virtual image of an object. Name the device which uses this principle.
What is a magnifying glass?
The maximum magnifying power of a convex lens of focal length 5 cm can be ______.
Define the term magnifying power of a simple microscope. How does it depend on the focal length of the lens used?
Why is the focal length of the lens, used as a magnifying glass, kept short?
Name the lens for which magnification can be 1. For what position of the object will the magnification be 1?
Copy and complete the following ray diagram.
An erect, magnified, and a virtual image is formed when an object is placed between the optical centre and principal focus of a lens.
(i) Name the lens.
(ii) Draw a ray diagram to show the formation of the image with the above-stated characteristics.
What is a magnifying glass (or a simple microscope)? Draw a ray diagram to show how a convex lens may be used as a magnifying glass. Where should the object be placed? State three characteristics of the image formed.
State two uses of magnifying glass.
