Optics Flashcards
Fermats principle of least time
The optical path length of the ray between two points is stationary with respect to small changes of the path
Light travels in _ in uniform medium
Straight lines
Law of relfection
The reflected ray lies in the plane of incidence, with the angle of reflection equal to the angle of incidence
Law of refraction
The refracted ray lies in the plane of incidence, with the angle of refraction related to the angle incidence by Snells law.
Positive R means
C is to the right of the lens
Negative R means
Its to the left
Positive lenses
Thicker in the middle than the edges. f is positive. (Bulge out more than they cave in). Always tries to make rays converge more than they did to start with
Real images form
After the lens
Virtual images form
Before the lens
Negative lenses
Thinner in the middle than the edges, they ‘cave in’ more than they ‘bulge out’ . Makes rays diverge more than they did to start with
Chromatic abberation
Focal length depends on refractive index, which depends on wavelength, so different colours get focused at different points, leading to fringing
Spherical aberration
Spherical lenses deviate from the “thin and paraxial” approximation. Light further from axis is focused closer to the lens than light closer to the axis, so light is not focused at a single point
Chromatic aberration mitigation
Use curved mirrors instead of lenses
Spherical aberration mitigation
‘Aspheric’ lenses
Superposition Principle
The disturbance, at any point in a linear medium is the algebraic sum of the separate constituent waves
