When an object is placed 10 cm in front of lens A, the image is real, inverted, magnified and formed at a great distance. When the same object is placed 10 cm in front of lens B, the image formed is real, inverted and same size as the object. (a) What is the focal length of lens A ? (b) What is the focal length of lens B ? (c) What is the nature of lens A ? (d) What is the nature of lens B ?

Open in App

Solution

Case 1 - Condition says the image is real, inverted but formed at a large distance.
this is followed only if the object is kept at focus, and the resultant focal length is 10cm for "A" lens.
Case 2 - Condition says that image is real, inverted and same size of object, which happens only if object is kept at centre of curvature. as radius of curvature becomes 10cm, focal length is 5cm for lens "B".

Both A and B are convex lenses, because both are giving a real image.

Suggest Corrections

Similar questions

A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find :

(a) the position of image, and

(b) the focal length of the lens

Q. (a) What type of lens is used as a magnifying glass?
(b) What type of lens is used to correct the defect of vision called myopia?
(c) A convex lens has a focal length of 10.5 cm. Where should an object be placed in front of this convex lens so as to obtain an image which is real, inverted and same size as the object?

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 ?

Q. An object is placed

15 c m

in front of a lens. The lens forms a real image three times magnified. Find out the image distance and the focal length of a lens?

Q. An object is placed at a distance of

10 c m

from a co-axial combination of two lenses

A

and

B

in contact. The combination forms a real image three times the size of the object. If lens

B

is concave with a focal length of

30 c m

, what is the nature and focal length of lens

A

Join BYJU'S Learning Program