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Question
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?
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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.
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A transparent refracting medium bounded by two surfaces, of which at least one is spherical, is called a:
The point near the centre of a thin lens through which a ray of light passes without appreciable deviation is called the:
The point on the principal axis where rays parallel to the principal axis actually meet after refraction, or appear to diverge after refraction, is called the:
The distance between the optical centre and the principal focus is called the:
In the Lens Maker's Formula, the symbols \[R_1\] and \[R_2\] denote:
For a thin lens, the magnification \[m\] in terms of image distance \[v\] and object distance \[u\] is given by:
According to the new Cartesian sign convention for lenses, the focal length of a concave lens is:
According to the new Cartesian sign convention for lenses, heights measured below the principal axis are taken as:
A ray directed towards the principal focus of a concave lens, after refraction, emerges:
If the refractive index of a liquid equals that of a glass lens (\[n_1 = n_2\]), the lens maker relation gives \[\frac{1}{f} = 0\]. This means the focal length of the lens becomes:
A lens with an infinite focal length behaves like:
