# Studyit

Hi! i have a few questions about this thing, for reference, i want an excellence : )

first of all, for ray diagrams, does it matter what way i draw the rays? eg, lets say im drawing a diagram with 2 light rays of someone looking at her knee. Do I draw the light rays ‘spaced’ on the knee and pointing ‘coming together’ on the eye, or visa versa, and how can I tell what way to draw them in different scenarios?

Also, how do you explain why something is a plane mirros is inverted/ laterally inverted, and are images in total internal reflection inverted/laterally inverted?

whats the difference between total internal reflection and reflection, and how many images does total interal reflection produce eg in a prism?

what happens when you look at something right from above eg spoon in water, why doesn’t it refract then?

thank you

Kia ora @mego,

first of all, for ray diagrams, does it matter what way i draw the rays? eg, lets say im drawing a diagram with 2 light rays of someone looking at her knee. Do I draw the light rays ‘spaced’ on the knee and pointing ‘coming together’ on the eye, or visa versa, and how can I tell what way to draw them in different scenarios?

I would draw one from each end/side of the object. For example if drawing rays coming from a tree to an eye I would draw one ray from the top of the tree, and another from the bottom, both converging on the eye. Make sure you use a ruler and indicate direction with an arrow (towards the eye)

Also, how do you explain why something is a plane mirros is inverted/ laterally inverted, and are images in total internal reflection inverted/laterally inverted?

This is a really good question, I’d love to get into it in far more detail but since your exam is tomorrow this ray diagram may help. To consider another perspective you could watch this great video, but I’d maybe wait until after your exam.

whats the difference between total internal reflection and reflection, and how many images does total interal reflection produce eg in a prism?

Reflection usually occurs on a shiny surface and represents a change in direction of a light ray, in which the angle of incidence equals the angle of reflection.

Total internal reflection only happens when light from a more optically dense medium (eg glass) arrives at an interface or boundary with a less optically dense medium (eg air), at an angle beyond the critical angle. As the light can’t be refracted (at the critical angle the ray is already being refracted to the maximum extent possible), all of the light reflects back into the more optically dense medium. This video does a good job of demonstrating. As for how many images, you’d only see an image if you were inside the more optically dense medium, such as under the surface of a swimming pool with a very flat surface. Then each object would potentially create one image. Yet another person next to you would see a slightly different image of the object.

what happens when you look at something right from above eg spoon in water, why doesn’t it refract then?

As the rays are arriving at the interface between the two media (water and air) at an angle of zero degrees to the normal (perpendicular to the surface) their speed changes but the direction does not. Move your eye to the side and rays from different parts of the spoon will hit the interface at different angles, and refract to differing extents, causing the distortion of the spoon. It’s not quite the same situation, but here’s a neat demonstration of refraction.

I hope that helps. Best wishes for your exam tomorrow!