Chap. 9 Sight and waves phenomena Flashcards
Explain the terms polarizer and
analyser
A polariser produces plane-polarised light from an unpolarised beam. An analyser is a polariser used to detect polarised light.
Calculate the intensity of a transmitted beam of polarized light using Malus’ law
Intensity of light is proportional to the amplitude^2.
I = I0 (cos theta) ^2
What is meant by polarized
light?
Light that propagates on only one plane.
State the Rayleigh criterion for images of two sources to be just resolved.
When the first minimums lie on top of the maximum intensities.
Students should know that the criterion for a circular aperture is
θ = λ 1.22/b.
State and explain the process of depth of vision and accommodation.
when focusing on a near object, ciliary muscles contract and taught fibres are slack. This makes the lens thicker and shorter.
When focusing on a faraway object, ciliary muscles relax and taught fibres pull the lens longer and thinner.
Describe what is meant by an optically active substance.
Students should be aware that such substances rotate the plane of polarization.
Describe the function of the rods and of the cones in photopic and scotopic vision.
Photopic: cones. Related to colour vision in normal lighting. Three different cone types (R, G, B)
Scotopic: rods. Black and white in dim light.
Colour blindness is caused by the failure of one or more types of cones to respond.
Discuss the effect of light and dark, and colour, on the perception of objects.
Students should consider architectural effects of light and shadow (for example, deep shadow gives the impression of massiveness). Glow can be used to give an impression of “warmth” (for example, blue tints are cold) or to change the perceived size of a room (for example, light-coloured ceilings heighten the room).
State that the retina contains rods and cones, and describe the variation in density across the surface of the retina.
Cones peak at the fovea, while rods are distributed more evenly, the maximums being around the cone peak.
Explain the formation of
one‑dimensional standing waves.
When two waves meet that are of the same amplitude and of the same frequency travelling in opposite directions
Describe what is meant by the
Doppler effect.
The change of frequency of a wave as a result of the movement of the source or the movement of the observer.
Describe the nature of standing
(stationary) waves.
Amplitude: all points on the wave have different amplitudes. the maximum amplitude is 2A at the antinodes. It’s zero at the nodes.
Energy is not transmitted.
All points between nodes are moving in phase.
Describe polarization by reflection.
This may be illustrated using light or microwaves.
The use of polarized sunglasses should be included.
A ray of light incident on a boundary between two media will be reflected and refracted. The reflected ray is always partially plane-polarised. If the refracted and reflected rays are at right angles to each other, then the reflected ray is completely plane-polarised.
What is brewster’s angle?
Brewster’s angle happens when the transmitted ray is 90° to the reflected ray. The angle gives us the angle of incidence needed for completely polarised light. Only for incident light in a vacuum
tan ø = n₂ (refractive index of the substance the light enters)
What is Malus’ law?
The change in intensity of light passing through a Polaroid analyser.
For polarised light incident on a polariser
I = I₀cos²θ
(I₀ = incident intensity, θ = angle between polariser axis and direction of electric field). For unpolarised incident light the transmitted intensity is I₀ / 2.
