Answer:
air or vacuum is the least refractive index medium of most rare medium
all other medium has more value of refractive index and hence the speed will be less than the speed of the air
Explanation:
As we know that speed of light in any medium and speed of light in air is related to each other by the equation

here we know that

[tex]\mu [tex] = refractive index of the medium
so we know that air or vacuum is the least refractive index medium of most rare medium
all other medium has more value of refractive index and hence the speed will be less than the speed of the air
A constant velocity means the acceleration is zero.
Neither the opposite direction (left) or its slowing down. Hope this helps
Answer:
The internal energy of a substance is equal to the total amount of potential energy and kinetic energy of ALL the particles in the substance.
For example, when the temperature increases (more temperature means more energy), the kinetic energy of the particles in the substance increases.
And when we reach a point near a change of phase (like near fusion point) there is energy used to break the bonds between the particles, then we have an increase in potential energy.
Then we could write the internal energy as:
U = ∑(KEₙ) + ∑(PEₙ)
Where ∑(KEₙ) and ∑(PEₙ) are the sums of the kinetic energy and potential energy of all the particles in the substance.