Q23 of 36 Page 379

A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 18 cm at a distance of 12 cm from it. Use lens formula to determine the position, size and nature to the image formed.

According to the question;

Object distance = -12cm;


Image distance = v;


Focal length = 18cm;


By lens formula;







⇒ v = -36cm.


Therefore, image is formed at 36 cm in front of lens.


Now;


Height of object h1= 5cm;


Magnification = =


Putting values of v and u


Magnification =


⇒


⇒


Height of image is 15 cm.


Thus, the image is virtual, enlarged, and erect and three times the size of object.


More from this chapter

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21

A concave lens has 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.

 22

What is meant by power of a lens? Name and define its S.I. unit.

One student uses a lens of focal length +50 cm and another of –50cm. State the nature and find the power of each lens. Which of the two lenses will always give a virtual, erect and diminished image irrespective of the position of the object?

 24

What is meant by ‘power of a lens’?

 24

State and define the S.I. unit of power of a lens.