Speed Of Light
Speed of light using fizeaus method C = 2Dnω/π = 4 Dnv
D is distance from the rotating wheel to the mirror
ω = angular speed of rotation of the wheel when image is completely unseen for the first time
N = number of teeth in the wheel
ω = 2πv, where v is linear frequency or number of rotations per unit time.
Foucault’s method to find speed of light
C = 4R2 [ωa / S(R + b)]
Where R is radius of the concave mirror
ω = the angular speed of plane mirror
A = distance between lens and source S
B = distance between plane mirrors and lens
S = shift in image
Michelson method to find speed of light
C = Dω N / 2π = DvN
Where
N = number of faces in a polygonal mirror
ω = angular speed of rotation
D = distance travelled by light between the reflections from polygonal mirror.
V = ω / 2π the linear frequency.
Fresnel distance zF = a2/λ where a is slit width
It is the minimum distance a wave has to travel before its deviation from straight path becomes significant.
Lamberts cosine law the surfaces which radiate according to lamberts cosine law are called perfectly diffused.
I = I0 cos θ
Luminous flux: - radiation emitted by a source has components corresponding to a wide range of wavelengths. Different components wavelengths have different energies and different brightness. The luminous flux is a quantity directly representing the total brightness producing capacity of the source. Its unit is in men. Luminous flux of a source of 1 / 685 W emitting monochromatic light of wavelength 555 nm is called 1 lumen that is, a 1W source emitting a monochromatic light of wavelength 555 nm emits 685 lumen.
Relative luminosity = luminous flux of a source of given wavelength / luminous flux of a 555 nm source of same power
Luminous efficiency = total luminous flux / total radiant flux = luminous flux emitted / power input to the source.
Luminous intensity or illuminating power (I) luminous flux per unit solid angle is called luminous intensity. Its unit is candela (cd)
I = dF / dω = F / 4 π ω ---> solid angle
1 candela is the luminous intensity of a black body of surface area 1 / 60 cm2 placed at the freezing temperature of platinum at a pressure of 101.325 Nm-2.
Illuminance (E) is the luminous flux incident per unit area.
E = df / dA unit lumenm-2 or flux (CGS unit phot)
Law of photometry:- a photometer is used to compare intensities of two sources
I1 / I2 = d12 / d22
Where d1 and d2 are distance of sources from the photometers.
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