Two light waves of equal wavelength, lambda, are emitted in phase from separate sources and propagate to a common point P. Light wave 1 must travel a longer distance (d1) than light wave 2 (d2) to reach point P, where d1 – d2 is equal to the path difference between the two light waves. If the two waves interfere constructively at point P, what must be true about the path difference between the two light waves?

The path difference must be equal to an integral (1 * lambda, 2 * lambda, n * lambda) number of wavelengths for constructive interference to occur.

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.

i believe the answer is electric potential.

explanation: