You are given two objects of identical size, one made of aluminum and the other of lead. You hang each object separately from a spring balance. Because lead is denser than aluminum, the lead object weighs more. Now you weigh each object while it is submerged in water. Will the difference between the weights of the aluminum object and the lead object in water be greater than, less than, or the same as it was when the objects were weighed in air? greater than

Explanation:

Volume of lead object = volume of aluminium object = V

mass of lead object > mass of aluminium object

When both the objects immersed in water, the buoyant force acting on both the objects.

Buoyant force = Volume immersed  x density of water x gravity

As the volume of both the objects is same, so the buoyant force acting on both the objects is same.

So, weight in air of lead object is more than the weight in air of aluminium object.  

see earlier

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.