optics and light

Convex lens – Object at infinity

Image forms at focus (F), real, inverted, highly diminished

Convex lens – Object beyond 2F

Image forms between F and 2F, real, inverted, diminished

Convex lens – Object at 2F

Image forms at 2F, real, inverted, same size

Convex lens – Object between F and 2F

Image forms beyond 2F, real, inverted, enlarged

Convex lens – Object at F

Image forms at infinity, real, inverted, highly enlarged

Convex lens – Object between F and optical center

Image forms on same side of lens, virtual, erect, enlarged

Concave lens – Object at infinity

Image forms at focus (F) on same side, virtual, erect, highly diminished

Concave lens – Object at any finite distance

Image forms between focus and optical center on same side, virtual, erect, diminished

Reflection

Bouncing back of light into the same medium

Refraction

Bending of light when it passes from one medium to another

Diffraction

Bending and spreading of light around obstacles or narrow openings

Angle of incidence

Angle between incident ray and normal

Angle of refraction

Angle between refracted ray and normal

Huygens’ theory

Every point on a wavefront acts as a source of secondary wavelets

Bifocal lens

Lens having two different focal lengths for near and distant vision

Bifocal lens – Near vision part

Lower convex part facilitates near vision

Aperture

Effective diameter of a lens or mirror through which light passes

Polychromatic light

Light consisting of many colours or wavelengths

Monochromatic light

Light consisting of a single colour or wavelength

Reflecting telescope

Telescope using mirrors; invented by Isaac Newton

Refracting telescope

Telescope using lenses; invented by Hans Lippershey

Minimum distance of distinct vision

25 cm for a normal human eye

VIBGYOR

Sequence of colours in visible spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red

Colour with maximum wavelength in VIBGYOR

Red

Colour with minimum wavelength in VIBGYOR

Violet

Colour deviated most during dispersion

Violet

Colour deviated least during dispersion

Red

Dim light room to bright light room

Iris contracts and pupil becomes smaller

Rayleigh scattering

Scattering of light by particles much smaller than wavelength

Reason sky appears blue

Rayleigh scattering of shorter wavelength blue light

Reason sunrise and sunset appear red

Longer wavelength red light scatters least

Dispersion of light

Splitting of white light into constituent colours

Specular reflection

Reflection from a smooth surface where parallel rays remain parallel