# Unit 3: Physics

## Light
 - `Light`: Electromagnetic radiation/waves, as light interacts with both electricity and magnets
 - Light travels at $`3.0 \times 10^8`$
 - `Energy`: Ability to do work
 - `Work`: Ability to move matter in space
 - Energy can be transferred and transformed, but not destroyed
 - Light behaves as a particle and/or a wave
    - Behaves as particle when travelling through a vacuum, which waves cannot do
    - Behaves as wave by forming "interference patterns", properties of light waves are also measurable
 - `Photon`: Light particle

### Properties of electromagnetic waves
<img src="https://sites.google.com/site/mrgsscienceclass/_/rsrc/1536069562258/about-science-class-1/physical-science-physics/energy-waves-1/Wave%20properties.PNG" width="500">

 - `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 <unit> (e.g., hertz (waves per second))
 - Visible light wavelengths are between 400-700 nm long

<img src="https://www.researchgate.net/profile/Jolanda_Patruno2/publication/280792916/figure/fig10/AS:669441209692171@1536618630777/Electromagnetic-spectrum-These-general-characteristics-above-indicated-are-valid-both.png" width="500">

 - 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

### Luminescence

|Type Of Luminescence|Description|Picture|
|:-------------------|:----------|:------|
|Incandescence|- Produces light by using high temperature to create heat and light. <br>- Occurs in light bulbs, where electricity passes through a **filament** using made of tungsten it becomes so hot that it gives off visible light<br>- 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. <br>- This is makes this process very inefficient <br>- Examples include <br>- incandescence light bulbs<br>- burning candle<br>- lit sparks flying off a grinder|<img src="https://i.stack.imgur.com/rSUeI.jpg" width="300">|
|Electric Discharge|- The process of producing light by passing electric current through a gas. Different gases produce different colours when electricity is passed through<br>- Examples include: <br>- Neon light signs <br>- Lightning (in this case, the gas is air)|<img src="https://i.ytimg.com/vi/r-E3vw5F8sI/maxresdefault.jpg" width="300">|
|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<br>- This is different than `Fluorescene`, as the light is released over a period of time<br>- Often described as `glow-in-the-dark` materials<br>- Examples include: <br>- glow in the dark watches, stickers, clocks etc|<img src="https://sc01.alicdn.com/kf/HTB1etspiDqWBKNjSZFxq6ApLpXaD/Glow-In-The-Dark-Dinosaur-Toy.jpg_350x350.jpg" width="300">|
|Fluoresence|- Process of producing light immediately as a result of the absorbtion of `ultraviolet` light<br>- Detergent manufacturerse often add flourescent dyes to make washed shirts more brighter<br>- This is process is even apparent in visible light because normal daylight includes a small amount of `ultraviolet` light<br>- 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.<br>- Fluorescent lights 4-5 more efficient than incandescent bulbs<br>- Examples include: <br>- Fluorescent lights|<img src="http://sdhydroponics.com/wp-content/uploads/2012/05/PastedGraphic-21-1.png" width="400">|
|Chemiluminescence|- The direct production of light as the result of a chemical reaction with **little** or **no heat** produced<br>- Light sticks is glow because when snapped, the 2 chemicals react with each other to produce light. <br>- 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. <br>- Examples include: <br>- Light sticks|<img src="https://www.thoughtco.com/thmb/1GoRbw0r-1kWPkmFey9BmR3H7Dw=/768x0/filters:no_upscale():max_bytes(150000):strip_icc()/flasks-with-glowing-liquids-520120820-594044535f9b58d58a548082.jpg" width="500">|
|Bioluminescence|- The production of light in living organisms as the result of `chemiluminescence`<br> Examples include: <br>- Fireflies<br>- fungi<br>- marine invertebrates<br>- fish<br>- glow-worms<br>- certain bacteria|<img src="https://www.hakaimagazine.com/wp-content/uploads/header-bioluminescence_0.jpg" width="300">|
|Triboluminescence|- The production of light from **friction** as a result of scratching, crushing, or rubbing certain cystals<br>- Examples include: <br>- Rubbing twoquartz crystals together will produce light due to triboluminescence|<img src="https://i.ytimg.com/vi/MzBXXmcaf2M/maxresdefault.jpg" width="300">|
|Light-Emitting Diode (LED)|- light produced as a result of an electric current flowing in **semiconductors**. <br>- **semiconductors** are materials that allow an electric current to flow in only one direction<br>- When electricity flows in the allowed direction, the LEd emits light<br>- **Does not** produce much **heat** as a by-product, nor require a **filament**, and is more energy efficient<br>- Examples include<br>- LED lights<br>- christmas tree lights<br>- illuminated signs<br>- traffic lights|<img src="https://d114hh0cykhyb0.cloudfront.net/images/uploads/rgb-fast-color-changing-led01.jpg" width="300">|



 - Things that emit light fill in here plz thanks

### 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

<img src="https://www.researchgate.net/profile/Merlin_John2/publication/293415482/figure/fig1/AS:326758030168064@1454916593825/Ray-diagram-for-image-formation-of-a-point-object.png" width="500">

 - `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

<img src="https://qph.fs.quoracdn.net/main-qimg-c84654e146945deec5ee6491cb547873.webp" width="500">

 - `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

<img src="https://www.physicsclassroom.com/Class/refrn/u14l3b2.gif" width="500">