Comprehensive Study Notes on Optics and Optics and Reference Guide to Optics Guide

Fundamental Properties of Light and Light Sources

• Definition of Optics: Optics is the scientific study or theory of light.

• Light Sources: To obtain light, a light source is required. Examples include:

  • Modern Sources: Light bulbs and fluorescent tubes.

  • Historical Sources: Torches, oil lamps, and kerosene lamps.

  • Primary Source: The sun remains our most important light source. In the past, it was the only source available.

• Solar Radiation Categories: The sun emits three distinct types of radiation:

  • Visible Light: The only type perceptible to the human eye.

  • Infrared Radiation: Perceived as heat.

  • Ultraviolet (UV) Radiation: Responsible for tanning and sunburns.

• Energy Transformation in Lamps:

  • Incandescent Bulbs: The filament is heated until it emits light. Electrical energy is converted into both heat and light. Light is a form of energy.

  • Fluorescent Tubes: These do not contain a filament. They contain a gas that emits ultraviolet radiation when connected to a voltage source. Since the human eye cannot see UV rays, the inside of the tube is coated with a specific fluorescent substance (‐lysmne‐) that emits visible light when hit by UV rays.

• The Speed of Light: Light travels at incredibly high speeds, taking time to travel from a source to the eye.

  • Comparison: If an astronaut could travel at the speed of light, they would circle the Earth seven times in a single second.

  • Speed in a Vacuum/Air: Approximately $300,000\,km/s$.

  • Speed in Water and Glass: Approximately $200,000\,km/s$ (described as ‐slower‐).

  • Sun-to-Earth Travel Time: Despite the high speed, it takes more than $8$ minutes for light to travel from the sun to the Earth.

• Rectilinear Propagation: Light rays spread along straight lines. Because light travels in straight lines, we cannot see around corners or behind mountains.

• Shadow Formation: If a pencil is placed between a light bulb and a screen, it creates a dark shadow. This shadow exists only because light rays travel in straight lines rather than bending around the object.

• Diagramming Light: In figures, light rays are drawn as straight lines with arrows indicating direction.

Reflection and Plane Mirrors

• Visibility of Objects: We see light sources because they emit light. We see non-luminous objects because their surfaces reflect (bounce back) a portion of the light hitting them. When reflected rays reach our eyes, the object effectively acts as its own light source.

• Reflectivity: Surfaces with higher reflectivity appear brighter. A black surface appears black because it reflects a very small portion of the incident light.

• Regular vs. Irregular Reflection:

  • Regular (Specular) Reflection: Occurs on smooth surfaces like mirrors. Parallel incident rays remain parallel after reflection. These surfaces are hard to see themselves; you see the image in the mirror, but not the surface of the mirror glass.

  • Irregular (Diffuse) Reflection: Occurs on rough surfaces (e.g., a sheet of paper seen under a microscope). Rays are reflected in many different directions, allowing us to see the object itself.

• The Law of Reflection:

  • Normal: An imaginary line drawn perpendicular to the surface at the point where the light ray hits.

  • Angle of Incidence ($i$): The angle between the incident ray and the normal.

  • Angle of Reflection ($r$): The angle between the reflected ray and the normal.

  • The Law: A light ray is always reflected such that the angle of incidence equals the angle of reflection ($i = r$). This behavior is compared to a hockey puck bouncing off the boards.

• Image Formation in Plane Mirrors: The image appears to be the same distance behind the mirror as the object is in front of it. The brain perceives light as traveling in a straight line from a point behind the mirror where the extensions of the reflected rays meet.

Curved Mirrors (Buktiga speglar)

• Mirror Terminology:

  • Principal Axis (Huvudaxel): A line passing through the center of the mirror.

  • Focal Point/Focus (F): The point where parallel rays meet (or appear to come from) after reflection.

  • Focal Length (Brnnvidd): The distance between the center of the mirror and the focal point.

• Concave Mirrors (Intbuktade): They collect or converge incoming rays.

  • Near view: Produces an enlarged image (e.g., shaving or makeup mirrors).

  • Distant view: Produces a diminished, upside-down (inverted) image.

  • Focal point: Parallel rays hitting a concave mirror converge at the focal point $F$.

  • Headlights: Placing a light source exactly at the focal point of a concave reflector causes the mirror to send out a beam of parallel rays. High beams (Helijus) use this; low beams (Halvljus) use a shielded filament to illuminate only the upper part of the reflector, directing light closer to the ground to avoid blinding others.

• Convex Mirrors (Uttbuktade): They spread or diverge incoming rays.

  • Image Properties: Always produces a diminished, upright image.

  • Applications: Used as rear-view mirrors on vehicles. The diminished image provides a larger field of vision, allowing the driver to see a wider area.

  • Focal point: The focal point lies behind the mirror. Reflected rays appear to originate from this point.

Refraction of Light

• Phenomenon: Light changes direction (refracts) when passing from one medium to another (e.g., air to water). This causes an oar in water to look broken or an object on the seabed to appear shallower than its actual depth.

• Optical Density:

  • Optically Denser Medium: Water and glass are optically denser than air.

  • Toward the Normal: When light moves from an optically thinner medium (air) to a denser one (water/glass), it refracts toward the normal. The angle of refraction ($b$) is smaller than the angle of incidence ($i$).

  • Away from the Normal: When light moves from an optically denser medium to a thinner one, it refracts away from the normal (b > i).

  • Perpendicular Incidence: Rays hitting a boundary at a right angle ($90^\circ$) pass through without refracting.

Total Internal Reflection and Fiber Optics

• Process: When light moves from an optically denser to a thinner medium, a portion is always reflected. As the angle of incidence increases, the reflected ray becomes stronger.

• Critical Angles:

  • Water to Air: If the angle of incidence is $49^\circ$ or greater, all light is reflected back into the water.

  • Glass to Air: If the angle of incidence is $42^\circ$ or greater, all light is reflected (total reflection).

• Prisms: Right-angled prisms utilize total reflection. In binoculars, they are used to flip images right-side up. Bicycle reflectors contain many small prisms that reflect light back toward the source (e.g., car headlights).

• Fiber Optics:

  • Description: Thin glass fibers (‐hrstr‐ width) that guide light via multiple total internal reflections.

  • Medical Use: To photograph or study internal organs (stomach, heart).

  • Telecommunications: Use of ‐optokabel‐. Electrical signals are converted to light pulses (lasers), sent through fibers, and converted back at the receiver. Advantages include very thin/light cables, immunity to electrical interference, and high capacity ($10,000$ simultaneous calls through two fibers).

Lenses and Magnification

• Types of Lenses:

  • Positive/Convex Lenses: Thicker in the middle than at the edges. Also called convergent or ‐samlingslins‐. They refract parallel rays to a focal point. Marked with a ‐+‐ sign (e.g., $+15$ means a focal length of $15\,cm$).

  • Negative/Concave Lenses: Thinnest in the middle. Also called divergent or ‐spridningslins‐. They spread parallel rays so they appear to come from a focal point in front of the lens. Marked with a ‐-‐ sign (e.g., $-10$ means a focal length of $10\,cm$).

• Optical Center: A ray passing through the exact midpoint of any lens passes through without refracting.

• Magnifying Glass (Lupp): A positive lens used to enlarge small text/objects. The object must be just inside the focal point. A ‐lupp‐ can provide approximately $25\times$ magnification.

Lighting and Lux

• Unit of Measurement: Lighting is measured in lux.

• Luxmeter: An instrument used to measure lighting. A camera’s exposure meter is a type of luxmeter.

• Lighting Quality: Higher brightness and proximity to the source increase lux levels. Sharp shadows are caused by single strong sources; softer lighting is achieved by using multiple lamps, matte bulbs, or lampshades.

• Recommended Lux Values:

  • General lighting, living room: $80\,lux$

  • General lighting, kitchen / Gymnasiums: $150\,lux$

  • Classrooms: $300\,lux$

  • Office work / School blackboard / Reading / Demonstration table: $500\,lux$

  • Drafting and drawing work: $1000\,lux$

Color and the Spectrum

• Prism Experiment: Passing white light through a clear glass prism creates a spectrum: red, orange, yellow, green, blue, indigo, and violet. This proves white light is a mix of all colors.

• Color Perception: The color we see depends on which colors are reflected and which are absorbed (sucked up). A red car reflects red light and absorbs all other colors. Black surfaces absorb all light.

• Color Conditions: An object’s color depends on the light source (e.g., clothes look different in daylight vs. fluorescent shop lights).

• Rainbows: Created by the refraction and reflection of sunlight in water droplets. You must stand with your back to the sun to see one.

• Reconstituting White Light: Spinning a color disk quickly makes it appear white, as the eye merges the colors.

Polarization and Lasers

• Polarized Light: Ordinary light vibrates in all directions. Polarized light vibrates in only one direction.

• Polaroid Glasses: Prevent blinding reflections from wet roads by blocking horizontal vibrations. They are most effective against reflected light, not direct sunlight.

• Lasers: Developed in the USA in the $1950$s.

  • Properties: Monochromatic (one absolute color/wavelength) and perfectly parallel rays that do not diverge over long distances.

  • Applications: Distance measurement (to the moon or for manufacturing quality), checking material thickness, surgery (welding a detached retina, laser scalpel), cutting hard materials (metal/ceramics) by vaporization, speed control (police LIDAR), and CD players.

Printing and Television Technology

• Four-Color Printing (Fyrfrgstryck):

  • Originals are scanned into four films: Red (Magenta), Yellow, Blue (Cyan), and Black.

  • Images are built of small ‐raster‐ points. If a yellow and blue dot overlap, the eye perceives green.

• Television:

  • The camera splits light into Red, Green, and Blue (RGB).

  • The screen has a layer of about one million phosphor dots grouped in threes (one R, one G, one B). Electron beams hit these points; their relative intensity determines the perceived color.

The Human Eye and Vision Defects

• Anatomy: Cornea (‐hornhinna‐), aqueous humor (‐kammarvatten‐), lens, and vitreous body (‐glaskropp‐) together act as a positive lens. The pupil acts as an aperture (opening in dark, closing in bright light).

• Accommodation: The lens changes thickness (becoming more convex for near objects) to focus on varying distances. Objects closer than $25\,cm$ usually appear blurry.

• Defects and Correction:

  • Farsightedness (Long-sightedness): Eyeball is too short. Image forms behind the retina. Corrected with positive lenses.

  • Nearsightedness: Eyeball is too long. Image forms in front of the retina. Corrected with negative lenses.

  • Presbyopia (lderssynthet): Age-related decrease in accommodation ability.

• Diopters: Unit of lens power.

  • $\text{Power in diopters} = \frac{1}{\text{Focal length in meters}}$

  • Example: $f = 0.5\,m \rightarrow 2\,diopters$. $f = 25\,cm (0.25\,m) \rightarrow 4\,diopters$.

  • Negative lenses use a minus sign (e.g., $f = 1/3\,m \rightarrow -3\,diopters$).

Optical Instruments

• Kikare (Telescope/Binoculars): Simple ones use an objective lens and an eyepiece (‐okular‐) (both positive) but produce inverted images. Prism binoculars use total reflection to flip the image upright.

• Microscope: Uses a system of lenses to magnify tiny objects like cells. Light microscopes magnify up to $1,000\times$; electron microscopes use electrons to reach $100,000\times$ magnification.

• Projectors: Use a condenser lens system to gather light onto a slide (‐diabild‐) and an objective to project the enlarged image onto a screen.

• Camera: A light-tight box. The aperture (‐blndare‐) regulates the amount of light; the shutter (‐slutare‐) regulates the exposure time (typically $1/60$ second for still subjects).