# Light In this unit: Properties of light Types of light Reflection

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Light In this unit: Properties of light Types of light Reflection
Colours Refraction

Light In the simplest terms what is light?
light is the form of Energy that we can see. light is part of the electromagnetic spectrum of energy

Types of Light Natural Light Sun Candles or Oil Lamps Wood (fire)
Bioluminescence (light produced by living organisms) Firefly, Angular Fish

Types of Light Artificial Light Incandescent bulbs Florescent bulbs
Phosphorescence stored and released later. Ex. paint Chemiluminescence A chemical reaction, Ex. glow sticks

Cost of Light If we use light or sources of light then we must also be prepared to pay for the source of the light! How would the cost of light be calculated? What energy source is used to produce most artificial light? So the cost of light is the cost of the electrical energy used to produce it.

Cost of Light Electrical energy costs money to produce. A watt is a unit of electrical power. The cost is calculated by how much of the electrical energy is used over a certain period of time. Calculations are made in kW.h's. 1 kW.h is 1000 watts of electrical energy operating for 1 hour.

Convert 60W to kW by dividing by 1000 Calculate the number of kW hours
Example: Calculate the cost of leaving a 60W light bulb on for 10 hours. Convert 60W to kW by dividing by 1000 Calculate the number of kW hours To complete the calculation we need to know how much is charged per hour. 60 W / 1000 = 0.06 kW 0.06 kW x 10 hours = 0.6 kW.h

Cost of Light \$0.48/10 hour period
Calculate the cost by multiplying the number of hours by the cost per kW.h If the cost per kW.h is \$0.08 (4.8 cents - or about 5 cents) Now multiply this by10 hours The cost of electricity to operate the 60W light bulb for 1 hour would be time x Cost 0.6 kW.h x \$0.08 = \$0.048 \$0.048 x 10 hours= \$0.48/10 hour period

Cost of Electricity Complete questions #’s 1a, 1b, 1c, and #2 from the BLM sheet 3-3 Answers: 1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 7.2¢ 1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 36¢ 1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 28¢ 2. There are about 226 days between October 8 and May 22. Cost = 1 kW x 226 days x 12 h/day x 8¢/kW•h = \$216.96

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.

Light travels much faster than sound. For example:
Thunder and lightning start at the same time, but we will see the lightning first. 2) When a starting pistol is fired we see the smoke first and then hear the bang.

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 objects Reflectors

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

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

Angle of incidence = Angle of reflection
The Law of Reflection Angle of incidence = Angle of reflection In other words, light gets reflected from a surface at ____ _____ angle it 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: 2) A car headlight 1) A periscope

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 ROY G BIV

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 red and green makes yellow Adding all three makes white again

Only red light is reflected
Seeing colour The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: Homework 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 A white hat would reflect all seven colours: 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: Shirt looks red White light Shorts look blue

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

Some further examples:
Object Colour of light Colour object seems to be Red socks Red Blue Black Green Blue teddy Green camel Magenta book Homework

Using filters Red Filter
Filters can be used to “block” out different colours of light: Red Filter Magenta Filter

Investigating filters
Colour of filter Colours that could be “seen” Red Green Blue Cyan Magenta Yellow

Color Mixes Well

Red Blue Green White Yellow Cyan Magenta

Words – speed up, water, air, bent, medium
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 water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent, medium

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