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Tahsili Physics (Light) Cheat Sheet by

2024 Tahsili Physics: Light


Engine­ering optics
the study of how light interacts with matter
Luminous Flux
the measure of the total amount of energy radiated per second from a light source in all directions (measured in lumens (lm)
a measure of the light that falls on a surface (measured in lux (lx))
Illumi­nation Formula
E = P/4πr2 (E = illumi­nation, P = luminous flux, r = distance)
the spreading of waves around barriers
the restri­ction of light to one direction
Primary colours

Charac­ter­istics of Spherical Mirrors

depends on position
virtual, upright, smaller
concave properties
infinitely large
real, inverted, highly diminished at focus
at focus
real, inverted, infinitely enlarged (no image)
beyond focal point
virtual, erect, enlarged image
2x the focal length
real, inverted, same size
before focal point = inverted and smaller
after focal point = erect and larger
virtual images cannot be collected on screen

Spherical Lenses

convex lens
collects light
concave lens
scatters light
the ratio of the image's length to the object's length
Magnif­ication formula
M = hi / ho or -di / do ( M is -ive if its real )
1/f = 1/di + 1/do


when two waves superi­mpose to form a wave with a higher or lower amplitude
young's double slit experiment
explains interf­erence; uses monoch­romatic light to create dark and light bands
λ = xd/L

Reflection Off a Plane

Reflection Law
incident angle = reflected angle
Properties of a plane image
1- virtual
2- upright
3- same size
4- horizo­ntally inverted
5- same distance

Spherical mirrors

concave mirror
collects light rays (used in telescope)
convex mirror
scatters light rays (sides of cars)
Principal Axes
center line
Focus / focal point
the point at which light rays appear to converge
Focal Length
the distance between the center of the mirror and the focus
focal length formula
f = r/2 (r = radius of curvature)

Refraction of Light

the bending of light through a medium
snell's law
n1sinθ1 = n2sinθ2 (n is the refractive index)
refraction index
n = c/v (c is the speed of light, v is the speed of light in the medium)
complete reflection
reflection within a medium that occurs when the angle of incidence is greater than the critical angle
critical angle
the angle of incidence that causes the reflected angle to have 90 degrees
complete reflection applic­ations
optical fibers
an optical illusion caused by a difference in temper­ature that creates refraction
when light is scattered by water droplets

Sight defects

farsig­hte­dness (long focal length)
corrected with a convex lens
nearsi­ght­edness (image forms in front of retina)
corrected with concave lens


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