7. an elevator descends at a constant velocity. which of the following is true? a. the total energy of the elevator is conserved because energy is always conserved. b. the total energy of the elevator is not conserved because a non-conservative force does work on the elevator. c. the total energy of the elevator is conserved because no net external force acts on the elevator. d. the total energy of the elevator is not conserved because a net external force acts on the elevator.

the amount of current in the coil

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.