Light

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Light by

1. Refraction

1.1. Terminology

1.1.1. Refraction: when light is ABSORBED into a transparent surface, and bends through it

1.1.2. Angle of refraction: depends on optical density

1.1.2.1. Higher o.d. = lower transmittance = bend more

1.1.2.2. If angle of incidence is 90 degrees, zero refraction

1.1.2.3. r becomes smaller when there is a more optically dense medium

1.1.3. Only between 2 different interfaces e.g. air and water

1.1.3.1. Path taken is the same whether from water to air or air to water (REVERSIBILITY OF LIGHT)

1.2. Snell's Law

1.2.1. sin(i divided by sin(r = n AKA refractive index

1.2.2. if light travels from air to water, then express as air

1.2.3. i > r

1.3. Critical Angle

1.3.1. i in a denser medium where r = 90 degrees

1.3.2. All light reflected at interface: optical density is too damn high

1.3.3. 100% of light reflected, no absorption

1.4. Ray diagram: Refraction

1.4.1. Draw virtual image

1.4.1.1. mark out one point on object

1.4.1.2. draw another point 1/4 of total distance above first point

1.4.1.3. draw with broken lines

1.4.2. 2 rays: from image point to eye

1.4.2.1. Object: take into consideration r

1.4.2.2. Image: straight lines

1.4.2.3. Below interface: broken line

1.4.2.4. Above interface: straight line

2. Reflection

2.1. Theoretical

2.1.1. Terminology

2.1.1.1. Incident ray: ray that strikes the surface

2.1.1.2. Reflected ray: ray reflected off surface

2.1.1.3. Normal: imaginary line, perpendicular to surface, at O

2.1.1.4. O: point where incident ray strikes surface

2.1.1.5. i: angle between incident and normal

2.1.1.6. r: angle between reflected and normal

2.1.2. Laws

2.1.2.1. 1. Incident, Reflected, Normal all lie in the same plane (use the same surface)

2.1.2.2. 2. i = r

2.2. Types

2.2.1. Specular: for smooth surface (image visible)

2.2.2. Diffused: for rough surface (no image)

2.3. Image characteristics

2.3.1. 1. same size

2.3.2. 2. same distance from mirror as object

2.3.3. 3. same orientation (if object is upright, image is upright)

2.3.4. 4. laterally inverted (left becomes right)

2.3.5. 5. virtual

2.3.5.1. doesn't exist

2.3.5.2. merely a projection: if light rays could go through the mirror then image is created

2.3.5.3. when we see something in the mirror, it is because a light ray travels from the image into our eyes

2.4. Different types of mirrors

2.4.1. Plane

2.4.1.1. see ^ above

2.4.2. Convex

2.4.2.1. Behind the mirror, same orientation, smaller, virtual

2.4.2.1.1. Light rays bounce off the mirror and gather at a focal point

2.4.3. Concave

2.4.3.1. If object is inside focal point:

2.4.3.1.1. Behind mirror, virtual, same orientation, larger

2.4.3.2. If object is outside focal point:

2.4.3.2.1. In front of mirror (same side as object), real, laterally inverted, smaller

2.5. How to draw

2.5.1. Steps

2.5.1.1. Draw image: it's at an equal distance as the object

2.5.1.2. 2 rays from image to eye (see rules on rays)

2.5.1.3. Another two rays from object to O

2.5.2. Rules

2.5.2.1. pencil, ruler for drawing

2.5.2.2. compass, ruler to find location of image

2.5.2.3. LABELLING

2.5.2.4. rays

2.5.2.4.1. solid: real

2.5.2.4.2. broken: virtual (image/normal)

2.5.2.5. object => mirror => eye

3. Colors

3.1. Mixing of color:

3.1.1. Primary

3.1.1.1. Red

3.1.1.2. Green

3.1.1.3. Blue

3.1.2. Secondary

3.1.2.1. Yellow (Red plus Green)

3.1.2.2. Magenta (Red plus Blue)

3.1.2.3. Cyan (Blue plus Green)

3.1.3. Filter

3.1.3.1. Remove color from light

3.1.3.2. Red filter removes Cyan (secondary color)

3.1.3.3. Magenta filter removes Green (primary color)

3.1.3.4. If red light goes through blue filter

3.1.3.4.1. Red shall not pass

3.1.3.4.2. No other color: light transmitted is black

3.2. Dispersion:

3.2.1. Split white light according to wavelength (visible spectrum)

3.2.1.1. Violet

3.2.1.2. Indigo

3.2.1.3. Blue

3.2.1.4. Green

3.2.1.5. Yellow

3.2.1.6. Orange

3.2.1.7. Red

3.2.2. How?

3.2.2.1. Refraction through prism

3.2.2.2. Each color slows down at different rates

3.2.2.2.1. Refracts at different angles

3.2.2.2.2. Red: longest wavelength: fastest, least refraction

3.2.2.2.3. Violet: shortest wavelength: slowest, most refraction

4. Lenses

4.1. Convex

4.1.1. Double convex

4.1.2. Plano convex

4.1.3. Positive meniscus

4.2. Types of images formed by convex (where u = object distance from C)

4.2.1. 1. where u is infinity or beyond 2F, the image is

4.2.1.1. real

4.2.1.2. upside down

4.2.1.3. smaller

4.2.1.4. left to right

4.2.1.5. uses: eye, telescope, camera

4.2.2. 2. where u = 2F

4.2.2.1. Real

4.2.2.2. Upside down

4.2.2.3. same size

4.2.2.4. left to right

4.2.2.5. uses: photocopier

4.2.3. 3. where f < u < 2f

4.2.3.1. Real

4.2.3.2. Upside down

4.2.3.3. Bigger

4.2.3.4. Left to right

4.2.3.5. Photograph enlarger

4.2.4. 4. where u =< f

4.2.4.1. Virtual (no img produced)

4.2.4.2. Upright

4.2.4.3. Magnified

4.2.4.4. Not laterally inverted

4.2.4.5. Telescope (eyepiece lens)

4.3. Principal rays

4.3.1. 1. Through C; no refraction

4.3.2. 2. Parallel to focal plane, passes through F

4.3.3. 3. Passes through F, passes through parallel

4.4. Terminology

4.4.1. Optical center; C (center of lens)

4.4.2. Principal axis: vertical line through C

4.4.3. Focal point (F); where the light rays converge to form img

4.4.4. Focal length (f); distance between F and C

4.4.5. Focal plane: horizontal line through C

4.5. Concave

4.5.1. Diverges light rays

4.5.2. Focal point is where the light rays gather... when extended backwards

4.5.3. Types

4.5.3.1. Double concave

4.5.3.2. Plano concave

4.5.3.3. Negative meniscus

5. Applications of Optics

5.1. Optical fibers

5.1.1. Telecommunications

5.1.1.1. glass fibre reflects laser containing signal all the way to a receiver unit

5.1.2. Endoscopy

5.1.2.1. Millions of small optic fibers connected to one control body

5.1.2.2. Optic fibers shine light, image is then processed by control body

5.1.2.3. Allows surgeries to involve a small hole to stick endoscope in (as opposed to large slash)

5.2. Prisms

5.2.1. A block of isosceles right-angled triangle shaped glass

5.2.1.1. As light enters the prism it is reflected at angle of 90 degrees

5.2.1.2. Arrange two in the same tube, get a periscope

5.2.1.3. Arrange two opposite each other, invert light 180 degrees, and see what's behind you

5.3. Inferior Mirage

5.3.1. Cool air is above hot air in desert

5.3.2. Total internal refraction: the blue of the sky is reflected into our eyes instead of the ground

5.3.3. We mistake this for a water body

5.4. Superior Mirage

5.4.1. When cold air is below warm air, and light rays on objects are projected into the sky