A tank filled with water has marks every 10 cm on one wall.

The refractive index is 1.33 for water in the tank.
You observe the marks out in air, from the opposite wall and with your eye level with the top of the water.

Which is the lowest or highest mark that you can see?

options
You can see all the marks
A) The mark at 10 cm

B)The mark at 20 cm
C)The mark at 30 cm

D)The mark at 40 cm

E)The mark at 50 cm

F)The mark at 60 cm

G)The mark at 70 cm

i think it shld be B

To determine which mark you can see from the opposite wall, we need to consider the laws of refraction.

When light travels from one medium (air) to another medium (water), it bends or changes direction due to the change in the refractive index. The refractive index of water is 1.33, meaning light travels slower in water than in air.

In this scenario, you are observing the marks in air from the opposite wall with your eye level with the top of the water. This implies that your line of sight would be at an angle to the marks on the wall.

To determine the lowest mark that you can see, we need to consider the critical angle of incidence. The critical angle is the angle of incidence at which light is refracted at exactly 90 degrees. Any incident angle greater than the critical angle will result in total internal reflection, meaning light will not pass through the interface but get reflected back.

The critical angle can be calculated using the formula:

critical angle = arcsin(1/n)

where n is the refractive index of the medium the light is traveling from (in this case, air).

For air-water interface, the critical angle can be calculated as:

critical angle = arcsin(1/1.33) ≈ 48.8 degrees

Now, since you are observing the marks from the opposite wall, the incident angle will be the angle between your line of sight and the normal to the wall. Since your eye is level with the top of the water, the incident angle will be zero degrees at that height.

As you go lower in the tank, the angle between your line of sight and the normal to the wall will increase. However, since the critical angle is less than 90 degrees, light will not undergo total internal reflection.

Therefore, you can see all the marks, including the mark at 10 cm (option A), the mark at 20 cm (option B), the mark at 30 cm (option C), the mark at 40 cm (option D), the mark at 50 cm (option E), the mark at 60 cm (option F), and the mark at 70 cm (option G).