Speed Of Light Assignment Help

Optical Physics - Speed Of Light

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

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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