highschool/Grade 10/Science/SNC2DZ/Unit 3: Physics.md

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

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

• 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
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