Optics: Topic 4 Vergence Relationship and Paraxial Approximation (Exam 1)

Source of Light

Any object capable of emitting light.

What are light rays?

Trajectories by which light is transported.

What is the law for the propagation of light?

In mediums that are homogeneous, lineal and isotropic; light travels in lineal trajectories.

What does isotropic mean?

“Equal in all directions”.

What is optical infinity?

The distance at which light rays entering an optical system or the human eye are parallel.

(for human eye; starts at 20 feet (6m) and beyond.)

Point Source of Light

The size of the source is light is much smaller than the distance of observation.

(emits light evenly in all directions from a SINGLE, infinitely small point in space)

Extended Source of Light

The size of the source of light large enough to have observable effects.

(emits light from MULTIPLE points across its surface)

What is an example of an extended source of light?

• Galaxies

• Eclipse

What is an example of a point source of light?

Stars.

What are the two main parts of a shadow?

• Umbra

• Penumbra

What is the umbra?

The dark core where all direct light is blocked.

What is the penumbra?

The lighter outer border where light is only partially blocked.

What is an interface?

The separation between two media.

(i.e. the separation between air and water)

What can happen after an incident light hits at an interface?

The light can turn into either reflected light or transmitted light.

What law is transmitted light governed by?

Snell’s Law.

What is the Law of Reflection?

States that the angle of incidence EQUALS the angle of reflection.

(Both angles measured relative to the perpendicular line to the surface.)

What is the Law of Refraction?

*Snell’s Law

Describes how a light ray bends when it passes from one transparent material into another. (one medium into another)

What is the Coplanar Law

The incident ray, the reflected ray, the transmitted ray, and the normal to the surface are on the same plane.

What is the Plane of Incidence?

The flat, imaginary surface that contains BOTH the incoming light ray, and the line perpendicular (normal) to the boundary where the light strikes.

What is the “normal” line?

An imaginary, straight line drawn at a 90-degree PERPENDICULAR angle to a surface at the exact point where a light ray hits it.

Index of Refraction formula

• n = index of refraction of the material

• c = speed of light in vacuum

• v = speed of light on the material

What is the index of refraction?

A number that shows how much a light wave slows down and bends when it enters a new material.

Index of refraction of water:

1.33

*Important for exam to remember!

Index of refraction of vacuum:

1.00

(exact; light is at full speed)

Index of refraction of air:

1.0003 (very fast)

What is Fermat’s Principle?

Tells us that light will always take the path that requires the shortest amount of time.

What did Fermat’s Principle prove?

That the angle of incidence equals the angle of reflection when light hits a flat mirror.

Positive Angles

An angle is positive if the ray must be rotated clockwise to reach the surface normal.

Negative Angles

An angle is negative if the ray must be rotated counterclockwise to reach the surface normal.