- `Amplitude`: Height from centre to crest/trough
- `Crest`: Peak of wave
- `Trough`: Base of wave
- `Wavelength`: Distance between two points on wave on the same plane
- `Frequency`: Waves passing per 
- Light always travels in a straight line
- **Longer** wavelength = **smaller** frequency = **less** energy
- **Shorter** wavelength = **higher** frequency = **more** energy
- **Higher** energy, **lower** penetration (e.g., 2.4 GHz vs 5 GHz Wi-Fi)
- `Luminous`: Emits light
- Non-luminous objects do not emit light
- `Colour`: Reflected parts of white light from non-luminous objects
- Blacks absorb all visible light while whites do the opposite
|Type of electromagnetic wave|Picture|Use/phenomena|
|:---------------------------|:------|:------------|
|Radio Waves|
|• AM/FM radio• TV signals
• cellphone communication
• radar
• astronomy (for example, discovery of pulsars)| |Microwaves|
|• telecommunications• microwave ovens
• astronomy (for example, background radiation associated with the big bang)| |Infrared light|
|• remote controls (eg DVD players and gamecontrollers)• lasers
• heat detection
• Astronomy| |Visible light|
|• human vision• rainbows
• astronomy (eg optical teloscopes, discovering the chemical composition of celestial bodies)| |Ultraviolet light|
|• causes skin to tan and sunburn • increases risk of skin cancer
• kills bacteria in food and water
• lasers
• stimulates production of Vitamen D
• Astronomy| |X-Rays|
|• medical imaging• security equipment
• cancer treatment
• astronomy (eg. study of black holes, binary star systems)| |Gamma Rays|
|• Cancer treatment• product of nuclear decay
• astronomy (eg. supernovas)| ### Luminescence |Type Of Luminescence|Description|Picture| |:-------------------|:----------|:------| |Incandescence|- Produces light by using high temperature to create heat and light.
- Occurs in light bulbs, where electricity passes through a **filament** using made of tungsten it becomes so hot that it gives off visible light
- It also emits `infrared` light that you feel as heat radiating from the bulb depending on the bulb only a tiny fraction is converted to visible light the rest is converted to `infrared` light.
- This is makes this process very inefficient
- Examples include
- incandescence light bulbs
- burning candle
- lit sparks flying off a grinder|
|
|Electric Discharge|- The process of producing light by passing electric current through a gas. Different gases produce different colours when electricity is passed through- Examples include:
- Neon light signs
- Lightning (in this case, the gas is air)|
|
|Phosphorescence|- The process of producing light by the absorption of `ultraviolet` light resulting in the emission of visible light over an **extended** period of time- This is different than `Fluorescene`, as the light is released over a period of time
- Often described as `glow-in-the-dark` materials
- Examples include:
- glow in the dark watches, stickers, clocks etc|
|
|Fluoresence|- Process of producing light immediately as a result of the absorbtion of `ultraviolet` light- Detergent manufacturerse often add flourescent dyes to make washed shirts more brighter
- This is process is even apparent in visible light because normal daylight includes a small amount of `ultraviolet` light
- Flourescent lights makes use of both `electric discharge` and `fluorescence`. The electric gas (usually mercury) produces ultra-violet light during electric discharge, which is then used to produce visible light.
- Fluorescent lights 4-5 more efficient than incandescent bulbs
- Examples include:
- Fluorescent lights|
|
|Chemiluminescence|- The direct production of light as the result of a chemical reaction with **little** or **no heat** produced- Light sticks is glow because when snapped, the 2 chemicals react with each other to produce light.
- Chemiluminescence does not rely on `electric discharge`, little heat produced, no moving parts and can be sealed with durable material, making it very useful in hazardous environments.
- Examples include:
- Light sticks|
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|
|Bioluminescence|- The production of light in living organisms as the result of `chemiluminescence`Examples include:
- Fireflies
- fungi
- marine invertebrates
- fish
- glow-worms
- certain bacteria|
|
|Triboluminescence|- The production of light from **friction** as a result of scratching, crushing, or rubbing certain cystals- Examples include:
- Rubbing twoquartz crystals together will produce light due to triboluminescence|
|
|Light-Emitting Diode (LED)|- light produced as a result of an electric current flowing in **semiconductors**. - **semiconductors** are materials that allow an electric current to flow in only one direction
- When electricity flows in the allowed direction, the LEd emits light
- **Does not** produce much **heat** as a by-product, nor require a **filament**, and is more energy efficient
- Examples include
- LED lights
- christmas tree lights
- illuminated signs
- traffic lights|
|
### Rays
- Light path can be tracked via arrrows
- `Normal`: Perpendicular line to an interface (e.g., mirror, medium boundary), intersecting where light reflects off
- `Angle of incidence`: Angle of light hitting reflective surface, relative to the normal
- `Angle of reflection`: Angle of light leaving reflective surface, relative to the normal
- Laws of reflection
- Angle of incidence = angle of reflection
- Light rays are on the same plane
- Types of reflection
- `Specular reflection`: All normals are parallel (e.g., reflection off mirror)
- `Diffuse reflection`: Not all normals are parallel (e.g., paper, not-mirrors)
## Mirrors
- A mininum of **two** incident rays are required to find an image
- Where rays converge describe image
- **Dotted** lines are used for light going beyond a mirror (as light does not actually travel there)
- `SALT`: Describes image
- `Size`: Relative to object
- `Attitude`: Orientation relative to object
- `Location`: Relative to mirror and/or object
- `Type`: Virtual (behind mirror) or real (in front of mirror)
### Plane mirrors
- `Object-image line`: Line perpendicular to plane mirror
- Distance is equal on both sides of mirror
- Describes location of object without requiring 2+ incident rays
- Banned
### Concave and convex mirrors
- `Concave mirror`: Curved mirror curving inwards in the direction of incident rays, like a cave
- `Convex mirror`: Curved mirror curving away from incident rays, like back of a spoon
- `Principal axis`: $`PA`$, line perpendicular to mirror when it hits it
- `Centre of curvature`: $`C`$, point where the centre of the circle would be if mirror was extended to a full circle
- `Focus`: $`F`$, point where all light rays focus on if incident rays are parallel to principal axis
- `Vertex`: $`V`$, point where principal axis meets mirror
- Imaging rules for curved mirrors:
- 1. Any incident ray **parallel** to the principal axis will reflect directly to or away from the **focus**
- 2. Any incident ray that would pass through the **focus** will reflect **parallel** to the principal axis
- 3. Any incident ray that would pass through the **centre** of curvature will reflect **back on the same path**
- 4. Any incident ray that reflects off the **vertex** reflect as if it were a plane mirror
**Characteristics of concave mirror images**
| **Object location** | **Size** | **Attitude** | **Location** | **Type** |
| :--- | :--- | :--- | :--- | :--- |
| Farther than $`C`$ | Smaller than object | Inverted | Between $`C`$ and $`F`$ | Real |
| At $`C`$ | Same as object | Inverted | On $`C`$ | Real |
| Between $`C`$ and $`F`$ | Larger than object | Inverted | Farther than $`C`$ | Real |
| At $`F`$ | N/A, lines do not converge | | | |
| Between $`F`$ and $`V`$ | Larger than object | Upright | Behind mirror | Virtual |
**Characteristics of convex mirror images**
| **Object location** | **Size** | **Attitude** | **Location** | **Type** |
| :--- | :--- | :--- | :--- | :--- |
| Anywhere | Smaller than object | Upright | Between $`F`$ and $`V`$/behind mirror | Virtual |
## Refraction
- Speed of light depends on its medium
- Light bending while transitioning from a slower to faster medium or vice versa
- Greater the change in speed, greater than change in direction
- Turns in direction of **leading edge**
- Analogy: Sleds slowing from one runner first when transitioning from snow to pavement
- **Slow -> fast** medium: Refracts **away** from normal
- **Fast -> slow** medium: Refracts **towards** normal
- `Angle of refraction`: Angle of light after interface, relative to normal
- Index of refraction: speed of light in vacuum / speed of light in medium
- $`n = \dfrac{c}{v}`$
- $`n_1 \sin\theta_{\text{incidence}} = n_2 \sin\theta_{\text{refraction}}`$
- Where $`n_{1}`$ and $`n_{2}`$ are the refractive indexes of two different media
- Snell's law: $`\dfrac{\sin\theta_2}{\sin\theta_1} = \dfrac{v_2}{v_1} = \dfrac{n_1}{n_2}`$
## Total internal reflection
- `Critical angle`: Angle of incidence that causes refracted ray to be perpendicular to normal
- TIR occurs when angle of incidence exceeds critical angle, causing near-100% reflection
- Happens only when refracting from **slow to fast**
- **Refraction is not perfect; some light is reflected during refraction**
- Reflected ray grows brighter as we reach critical angle, and refracted ray grows dimmer
- **Higher** index of refraction = **lower** critical angle
## Lens
### Thin lens equations
- Can be used to find **location** and **magnification** of images
$`\frac{1}{d_{o}} + \frac{1}{d_{i}} = \frac{1}{f}`$
- $`d_{o}`$: Distance of **object** from optical centre, always positive
- $`d_{i}`$: Distance of **image** from optical centre
- If positive, image is **real** and on the **opposite** side of the lens as the object
- If negative, image is **virtual** and on the **same** side of the lens as the object
- $`f`$: Distance of **focus** from optical centre
- Is positive in a converging lens
- Is negative in a diverging lens
$`M = \frac{h_{i}}{h_{o}} = -\frac{d_{i}}{d_{o}}`$
- $`h_{o}`$: Height of object
- $`h_{i}`$: Height of image
- If positive, image is **upright and virtual**
- If negative, image is **virtual** but on the same side of the lens as the object
- $`M`$: Magnification of image
- If positive, image is **upright and virtual**
- If negative, image is **inverted and real**
- If greater than 1, image is larger and farther from the optical centre than the object
- If less than 1, image is smaller and closer to the optical centre than the object