Question

Explain the following terms related to spherical lenses:; (i) optical center; (ii) centers of curvature; (iii) principal axis; (iv) aperture; (v) principal focus; (vi) focal length; (b) A converging lens has focal length of 12 cm. Calculate at what distance should the object be placed from the lens so that it forms an image at 48 cm on the other side of the lens.(All India - 2014)

Answer 1

Bhai tu sagar ban raha hai ya sagar hai

Answer 2

Spherical lenses

(i) Optical center:

• The central point of a lens is called as its optical center.
• It is denoted by symbol "O".

(ii) Centers of curvature:

• The center of spheres formed by concave lens or convex lens is called as centers of curvature.
• It is denoted by symbol "C".

(iii) Principal axis:

• An imaginary line passing through the both centers of curvature of lens it is called as principal axis.

(iv) Aperture:

• The exact diameter of the spherical lens in called as aperture.

(v) Principal focus:

• The incident ray that is parallel to the principal axis after refraction, either passes through or appear to pass through a point on principal axis.
• This point is called principal focus and it is denoted by symbol "F".

(vi) Focal length:

• In a lens the distance between optical center and principle focus is called its focal length.
• It is denoted by symbol "f".

(b) The object should be placed at 16 cm from the lens.

Given:

Focal length (f) = 12 cm

v = 48 cm

To find:

The value of 'u' = ?

Formula to be used:

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

Calculation:

$\frac{1}{12}=\frac{1}{48}-\frac{1}{u}$

$\frac{1}{u}=\frac{1}{48}-\frac{1}{12}$

$\frac{1}{u}=\frac{1-4}{48}$

$\frac{1}{u}=\frac{-3}{48}$

$\frac{1}{u}=\frac{-1}{16}$

$u = -16$

Conclusion:

The lens should be placed at 16 cm from the lens so that it forms an image at 48 cm on the other side of the lens.

Learn more about such concept

Show that the mirror formula for spherical mirrors also holds for a plane mirror too.

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