The distance of an illuminated object from its light source is doubled while the luminous flux remains constant. Which is true of the illuminance on the object?
A)The illuminance will be halved.
B)The illuminance will quadruple.
C)The illuminance will be multiplied by the square root of 2.
D)The illuminance will be quartered the

e) none of the above answers are correct

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it is a negative acceleration

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.