Lenses

Lens is an object, usually made of glass, bounded by one or two spherical surfaces.

Types of lens: (i) convex or converging lens (ii) concave or diverging lens

Lens formula : The relation between object distance u, image distance v, and focal length f of a lens is known as lens formula .

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

Len's maker's formula : The relation between focal length of a lens, radii of curvature of two surfaces and refractive index of the material is called lens maker's formula.

$\frac{1}{f}$ =( $μ$ -1)( $\frac{1}{R _{1}}$ + $\frac{1}{R _{2}}$ )

Combination of thin lens

$\frac{1}{F}$ = $\frac{1}{f _{1}}$ + $\frac{1}{f _{2}}$

Power of a lens is a measure of its ability to produce deviation of light.

Power of a lens, P= $\frac{1}{f}$

$P = P_{1} + P_{2} + P_{3} + ..........$

Magnification of a lens is defined as the ratio of the size of image produced by it to the size of the object.

m= $\frac{size of image}{size of object}$ = $\frac{I}{O}$ = $\frac{v}{u}$ = $\frac{f}{u - f}$ = $\frac{v - f}{f}$

Optical centre is the geometrical centre of the lens through which light never bends after passing through.

Displacement formula, $f = \frac{D ^{2} - X ^{2}}{4 D}$

Focal length of a lens depends on radius of curvature, refractive index of the lens and that of the surrounding medium.
An air bubble inside the water behave as diverging lens.
If one of the surface of a lens is painted to make a mirror, then it behave as a combination of two lens and one mirror.
Intensity of the images proportional to the square of the aperture of the lens.
Minimum distance between the real object and real image by a convex lens is four times the focal length.
If the object is kept between optical centre and the focus of a biconvex lens, then it behaves as a magnifying lens.
The plane perpendicular to the principle axis at the focal point is called focal plane.
A sun glasses has no power.
Depending on the refractive index of the surrounding medium, the nature of the lens can be changed.
If a portion of a lens is broken still, then it will form the complete images.