Geometrical Optics 1 Flashcards
(in words) What is Heroβs Principle?
Light undergoing a reflection from a plane surface, while propagating between 2 points takes the shortest path.
What is the law of reflection, which follows from Heroβs Principle?
sin ππ = sin ππ
(in words) what is Fermatβs Principle
For light passing from one medium to another (ni ~> nt), the light travels the path of least time from one point to the next.
How can Snellβs law be derived from Fermatβs Principle?
- time = distance over speed
- replace distances with paths the ray takes
- dt/dx minimises the time when = 0
- substitute in for sines of angles
- substitute in formula for refractive indices
What is the refractive index of a medium?
n is defined as the ratio of the velocity of light in a vacuum to the velocity of light in a medium
n=c/v
What is Snellβs Law?
ππ sin ππ = ππ‘ sin ππ‘
What is the Principle of Reversibility?
If a ray in an optical system is reversed then it will retrace the same path backwards.
For a plane mirror, what is the relationship between the image and the object distance?
image distance is equal to the object distance
Why is the image for a plane mirror called a virtual image?
None of the rays actually lie beyond the mirror surface
What are the consequences of having a virtual image?
A virtual image cannot be projected onto a screen because it is formed by the apparent intersection of diverging rays.
What is the sign convention for image and object distance for a plane mirror?
- The object distance s is positive because the object is on the same side as the incoming light
- The image distance sβ is negative because the image is not on the same side as the outgoing light
How do you define lateral magnification for a plane mirror?
m = yβ / y
- for a plane mirror y=yβ, so m = 1
What happens to an image formed by a plane mirror?
It is inverted
