- Trending Categories
- Data Structure
- Networking
- RDBMS
- Operating System
- Java
- MS Excel
- iOS
- HTML
- CSS
- Android
- Python
- C Programming
- C++
- C#
- MongoDB
- MySQL
- Javascript
- PHP
- Physics
- Chemistry
- Biology
- Mathematics
- English
- Economics
- Psychology
- Social Studies
- Fashion Studies
- Legal Studies

- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who

# A concave lens has focal length 15cm. If we want to get a sharp image on a screen placed at 10cm from the lens, then at what distance the object should be placed from the lens ?

Given:

Image distance, $v=-10 \mathrm{cm}$

Focal length, $f=-15 \mathrm{cm} \quad$ [f is -ve for a concave lens]

To find: We have to find the object distance, $u$

Solution:

Using lens formula,

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

we have,

$\frac{1}{u} =\frac{1}{v}-\frac{1}{f} $

$=\frac{1}{-10}-\frac{1}{-15}$

$=\frac{-3+2}{30}$

$=-\frac{1}{30}$

So, $u =-30 \mathrm{cm}$

Thus the object should be placed at a distance of $30 \mathrm{cm}$ from the lens on the left side.

- Related Articles
- A concave lens has focal length 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens.
- The focal length of concave lens is 15cm at what distance object should be kept so that image formed will be 10cm away from lens. Find magnification of object.
- A converging lens of focal length 5 cm is placed at a distance of 20 cm from a screen. How far from the lens should an object be placed so as to form its real image on the screen?
- A concave lens has a focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.
- A magnifying lens has a focal length of 100 mm. An object whose size is 16 mm is placed at some distance from the lens so that an image is formed at a distance of 25 cm in front of the lens.(a) What is the distance between the object and the lens?(b) Where should the object be placed if the image is to form at infinity?
- An object 50 cm tall is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
- A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray-diagram.
- The image of a candle flame placed at a distance of 36 cm from a spherical lens is formed on a screen placed at a distance of 72 cm from the lens. Identify the type of lens and calculate its focal length. If the height of the flame is 2.5 cm, find the height of the image.
- An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.
- An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Fine the position and nature of the image.
- A concave lens of 20 cm focal length forms an image 15 cm from the lens. Compute the object distance.
- A convex lens produces an inverted image magnified three times of an object placed at a distance of 15 cm from it. Calculate focal length of the lens.
- When an object is placed at a distance of 36 cm from a convex lens, an image of the same size as the object is formed. What will be the nature of image formed when the object is placed at a distance of:(a) 10 cm from the lens? (b) 20 cm from the lens?
- An object of 5.0 cm size is placed at a distance of 20.0 cm from a converging mirror of focal length 15.0 cm. At what distance from the mirror should a screen be placed to get the sharp image? Also, calculate the size of the image.
- An object is placed at a distance of 40 cm from a convex lens of focal length 30 cm. Find the position of the image.

Advertisements