If I put my finger in a glass of water or a glass of oil, which would make my finger look bigger and why?

I think it would be oil because of the why the light is refracted-a thicker medium would bend the light more than the water

Why don't you try it? A cup of vegetable oil, a cup of water. Science works best if we try to explain what is observed, not try to explain what we think.

Scientists have tried to define precisely the _____ since the metric system was introduced

You are correct! Submerging your finger in a glass of oil would make it appear bigger compared to a glass of water. This phenomenon occurs due to the difference in the refractive index of the two substances.

The refractive index is a measure of how much a substance can bend or refract light. Oil has a higher refractive index compared to water. When light passes from one medium to another (such as from air to water or air to oil), it changes direction due to the different refractive indexes.

In the case of your finger submerged in water, light traveling from the water to your finger and back to the air undergoes refraction at both interfaces. However, since the refractive index of water is closer to that of the human tissue, the bending of light is minimal, and your finger appears slightly magnified but not significantly larger.

When your finger is placed in oil, the higher refractive index of oil causes the light to bend more as it travels through the oil to your finger and back to the air. This increased bending leads to a greater magnification effect, making your finger appear larger compared to when it is submerged in water.

So, in summary, due to the difference in refractive indexes, oil is more effective at bending light and causing a magnification effect, making your finger appear bigger when submerged in it compared to water.