Light, Reflection, Refraction, Color, Galaxies, and Asteroids

Objectives:
- Describe reflection from a plane surface.
- Understand the law of reflection.
- Draw ray diagrams to show reflection.
Key Words: angle of incidence, angle of reflection, incident ray, law of reflection, normal (perpendicular), plane mirror, protractor, ray diagram, rays, reflection, set square, perpendicular.
Light travels in straight lines called rays.
Use a ruler and arrowhead to indicate ray direction.
Incident Ray: A light ray arriving at a mirror.
Normal: A line perpendicular to the mirror at the point where the incident ray meets the mirror.
The angle of incidence is measured between the incident ray and the normal.
Steps to Constructing Ray Diagrams:
1. Draw the incident ray and the mirror.
2. Extend the incident ray to meet the mirror.
3. Draw the normal (dashed line) perpendicular to the mirror.
4. Measure the angle of incidence (???).
5. Measure an equal angle on the other side of the normal for the angle of reflection (???). Draw the reflected ray.
Law of Reflection: The angle of reflection equals the angle of incidence.
Mirrors are used in everyday situations to see behind us, like in car mirrors.
Ray diagrams show how light from an object (e.g., a cyclist) reflects off a mirror to the driver's eye.

Objectives:
- Describe how light is refracted between air and glass/water.
- Describe how light changes speed between different substances.
- Draw ray diagrams to show refraction.
Key Words: angle of refraction, away from the normal, bent, distorted, lenses, medium, refraction, towards the normal
Refraction causes distortion when looking through water or wet glass.
Medium: A material that light passes through (e.g., air, glass, water).
The speed of light varies in different media:
- Air: $300,000$ km/s
- Water: $225,000$ km/s
- Glass: $200,000$ km/s
Refraction of Light: The change in direction of light as it passes from one medium to another due to a change in speed.
When light travels from air into glass or water, it slows down and bends towards the normal.
The angle of incidence is greater than the angle of refraction in this case.
When light travels from glass or water into air, it speeds up and bends away from the normal.
The angle of refraction is greater than the angle of incidence in this case.
Refraction can be a nuisance, causing unclear vision through wet windows. Windscreen wipers help by removing water drops.
Lenses in glasses and cameras use refraction to focus light.

Objectives:
- Learn how white light is made from many colors.
- Discover how dispersion of white light can be done with a prism.
- Recall the colors of white light in the correct order.
Key Words: dispersion, prism, spectrum, triangular
In 1666, Isaac Newton discovered that white light could be split into different colors using a triangular prism.
Spectrum: The range of colors in white light.
The seven colors in the spectrum, in order, are: red, orange, yellow, green, blue, indigo, violet.
Mnemonic: ROY G. BIV.
Dispersion: Splitting light into different colors.
Dispersion occurs because each color of light is refracted at a slightly different angle by a prism.
Violet light is refracted the most, and red light is refracted the least.
Rainbows are formed when water droplets in the air cause dispersion and reflection of sunlight.
- The sun must be shining and behind the observer.
- There must be rain or small drops of water in the air.

Objectives:
- Discover what happens when colors of light are added.
- Discover what happens when colors of light are subtracted.
- Discover why we see different colors.
Key Words: absorbed, coloured filters, cyan, magenta, non-luminous, primary colours, subtraction, transmit
Primary Colors of Light: Red, green, and blue.
These colors cannot be made by mixing other colors of light.
Adding primary colors:
- Red + Green = Yellow
- Red + Blue = Magenta
- Blue + Green = Cyan
- Red + Green + Blue = White
Screens produce different colors by combining primary colors.
Colored filters remove colors from light through subtraction.
A filter transmits light of its own color and absorbs other colors.
Example: A red filter transmits red light and absorbs other colors.
Non-luminous objects appear colored because they reflect certain colors and absorb others.
A white object reflects all colors equally.
A black object absorbs all colors and reflects none.

Objectives:
- Discover that galaxies contain dust, gas, stars and other solar systems.
Key words: elliptical galaxy, galaxy, irregular, spiral, stellar dust, universe
A galaxy is a large collection of stars, gas, and dust held together by gravity.
Our galaxy is called the Milky Way, which appears as a milky band across the night sky.
The Milky Way is a spiral galaxy.
There are an estimated $250,000,000$ stars in the Milky Way, including the Sun.
The universe contains many galaxies.
Other galaxy shapes include elliptical and irregular.
The closest galaxy to the Milky Way is the Canis Major Dwarf Galaxy (elliptical).
Galaxies contain stellar dust, gas, stars, and solar systems.
Stellar dust is found in space.
The gravity holding a galaxy together is very strong due to its large size and mass.
It would take over $100,000$ years to cross the Milky Way, even at the speed of light.
The mass of the Milky Way is estimated to be $1,500,000,000,000$ times the mass of the Sun.
Scientists estimate there are $100,000,000,000$ galaxies in the universe.

Objectives:
- Discover that asteroids are rocks that are smaller than planets.
- Know that scientists believe asteroids to be rocks left over from the formation of the Solar System.
Key words: asteroid belt, asteroids, craters, impacts
Asteroids are rocky objects that orbit the Sun.
They range in size up to $975$ km across, with the smallest studied at 2m across.
Most asteroids have irregular shapes.
Most asteroids in the Solar System are located in the asteroid belt between Mars and Jupiter.
There are millions of asteroids.
Ceres is the largest asteroid, with a diameter of $975$ km.
Asteroids are thought to be leftover rocks from the formation of the Solar System.
Scientists believe a large asteroid impacts Earth every $130,000$ years on average.