# The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. - Physics

Numerical

The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose?

#### Solution

Distance between the object and the image, d = 3 m

Maximum focal length of the convex lens = "f"_"max"

For real images, the maximum focal length is given as:

"f"_"max" = "d"/4

= 3/4

= 0.75 m

Hence, for the required purpose, the maximum possible focal length of the convex lens is 0.75 m.

Concept: Refraction at Spherical Surfaces and Lenses - Refraction by a Lens
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#### APPEARS IN

NCERT Physics Part 1 and 2 Class 12
Chapter 9 Ray Optics and Optical Instruments
Exercise | Q 9.19 | Page 346
NCERT Class 12 Physics Textbook
Chapter 9 Ray Optics and Optical Instruments
Exercise | Q 19 | Page 347
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