When light travels from air to water at an angle which of the following happens? a) the light slows down and it changes direction away from the perpendicular. b) the light slows down and it changes direction towards the perpendicular. c) the light speeds up and it changes direction away from the perpendicular. d) the light speeds up and it changes direction towards the perpendicular.

b) The light slows down and it changes direction towards the perpendicular.

Explanation:

Light travels at different speed in different mediums.

Refractive index is equal to velocity of the light 'c' in empty space divided by the velocity 'v' in the substance.

Or ,

n = c/v.

Light travels at a slower speed in water as compared to air because there are more number of interfering molecules in the path of the light in case of water as compared to liquid.

When a light travels from lower denser medium say water to higher denser medium say water, it bends towards the perpendicular as its speed reduces in that medium.

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =