What is light?

Light and Sound In this unit you need to know: 1)Properties of light 2)Reflection 3)Colours 4)Refraction 5)Properties of sound 6)Hearing

Part 1 – Properties of Light Light travels in straight lines: Laser

Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

How we measure light and it’s speed: Formula: Λ * f = c Λ (lambda) = wavelength F= frequency C = speed of light Wavelength * Frequency = Speed of Light

We see things because they reflect light into our eyes: Homework

Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objectsReflectors

Shadows Shadows are places where light is “blocked”: Rays of light

Properties of Light summary 1)Light travels in straight lines 2)Light travels much faster than sound 3)We see things because they reflect light into our eyes 4)Shadows are formed when light is blocked by an object

Part 2 - Reflection Reflection from a mirror: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

The Law of Reflection The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at an equal angle to the angle that hits it. The same !!!

Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

Using mirrors Two examples: 1) A periscope 2) A car headlight

Colour White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.

The colours of the rainbow: Red Orange Yellow Green Blue Indigo Violet

Adding colours White light can be split up to make separate colours. These colours can be added together again. The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding all three makes white again Adding red and green makes yellow

Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

A white hat would reflect all seven colours: A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light White light

Using coloured light If we look at a coloured object in coloured light we see something different. For example, consider a football kit: White light Shorts look blue Shirt looks red

In different colours of light this kit would look different: Red light Shirt looks red Shorts look black Blue light Shirt looks black Shorts look blue

Solve the speed equation for distance: Speed = Distance/Time, so Distance = Speed x Time, or D = S x T Decide on a length of time, in seconds (s), for which that you wish to calculate the distance light will travel. Example: How far will light travel in one hour? (1 hour = 3,600 s)

Calculate distance Substitute the appropriate values in for their variables in the distance equation to solve the problem. D = S x T, so D = 186,000 mi/s x 3,600 s = 669,600,000 mi Now….how the heck can we calculate distance?

The Equation 1 Parsec = × meters A unit of distance used in astronomy, equal to about 3.25 light years (3.08 × meters).

Angles 1 degree = 1° = 1/360 of a circle 1 arcminute = 1' = 1/60 of a degree 1 arcsecond = 1" = 1/60 of an arcminute = 1/3600 of a degree

Arcsecond You A B Angle = arcsecond

The Parallax A nearby star's apparent movement against the background of more distant stars as the Earth revolves around the Sun is referred to as stellar parallax.

The nearest star is proxima centauri, which exhibits a parallax of arcsec, and therefore is 1.31 parsecs away. proxima centauri Try these: Star #1: arcsecond of Star #2: arcsecond of Star #3: arcsecond of 0.987

Formula for speed of light ƛ * F = C ƛ (lambda) =Wavelength F = Frequency C = Speed of Light You will be given values to plug in

Alternate forms

Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in a glass of _____ it looks like this (draw it) In this case the light rays are slowed down by the _____ and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, medium, water, air, bent

By observing how much “red” there is in the wavelength of light from a given spot, we can tell if it’s moving toward or away from us.

Topics to know for the test Red shift Calculate the Parallax Calculate speed of light Properties of light Angles of incidence and reflection Lens types Arc angles Definitions Refraction vs. Reflection Color and how it works. Electromagnetic spectrum: colors and waves ƛ * F = C Wavelength * Frequency = Speed of Light

Sound – The basics We hear things when they vibrate. If something vibrates with a high frequency (vibrates very ______) we say it has a _____ pitch. If something vibrates with a low frequency (vibrates ______) we say it has a ____ pitch. The lowest frequency I could hear was… Words – slowly, low, high, quickly

Drawing sounds… This sound wave has a _____ frequency: This sound wave has a ___ _frequency:

Drawing sounds… This sound wave has a _____ amplitude (loud): This sound wave has a _____ amplitude (quiet):

Hearing problems Our hearing range can be damaged by several things: 1)Too much ear wax! 2)Damage to the auditory nerve 3)Illness or infections 4)Old age (not like Mr Richards)

Other sound effects… Like light, sound can be… 1)Reflected – sound reflections are called ______. 2)Refracted – this is why you might sound strange if you try talking underwater

The Ear Label your diagram with the following: These bones are vibrated by the eardrum This tube carries the sound towards the eardrum This part is used to help us keep our balance This part “picks up” the vibrations This part of the ear contains many small hairs with turn vibrations into an electrical signal This part connects the ear to the mouth This part “channels” the sound towards the ear drum How does “sound” get to the brain? How does the brain “hear it” (it has no ears)

The Ear (see handout)

So…..now we come to a problem. We can observe light and sound. We know their properties. We can measure their speeds. We know how to manipulate them. But……. How can we use them to measure distance?