LightLight

In this unit:

1) Properties of light2) Types of light3) Reflection4) Colours5) Refraction6) Reflection

LightLight

• 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 LightCost 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.

Example: Calculate the cost of leaving a 60W light bulb

on for 10 hours. 1. Convert 60W to kW

by dividing by 1000

2. Calculate the number of kW hours

3. 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

• 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 Cost0.6 kW.h x $0.08 = $0.048

• $0.048 x 10 hours=

• $0.48/10 hour period

Cost of ElectricityCost of Electricity

Complete questions #’s 1a, 1b, 1c, and #2 Complete questions #’s 1a, 1b, 1c, and #2 from the BLM sheet 3-3from the BLM sheet 3-3

Answers:Answers: 1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 1(a) Cost = 0.1 kW x 9 h x 8¢/kW•h = 7.2¢7.2¢ 1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 1(b) Cost = 1.5 kW x 3 h x 8¢/kW•h = 36¢36¢ 1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 1(c) Cost = 0.5 kW x 7 h x 8¢/kW•h = 28¢28¢ 2. There are about 226 days between 2. There are about 226 days between

October 8 and May 22. Cost = 1 kW x 226 October 8 and May 22. Cost = 1 kW x 226 days x 12 h/day x 8¢/kW•h = days x 12 h/day x 8¢/kW•h = $216.96$216.96

Part 1 – Properties of Part 1 – Properties of LightLight

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:

1) 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

Shadows

Shadows are places where light is “blocked”:

Rays of light

Properties of Light Properties of Light summarysummary

1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect

light into our eyes4) Shadows are formed when light is

blocked by an object

Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

In other words, light gets reflected from a surface at ____ _____ angle it hits it.

The same !

!!

Clear vs. Diffuse ReflectionClear 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 mirrorsUsing mirrorsTwo examples:

1) A periscope

2) A car headlight

ColourColour

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:The colours of the rainbow:

RedOrangeYellowGreenBlue

IndigoVioletRROOYY GG BBIIVV

Adding coloursAdding coloursWhite 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 colourSeeing colourThe 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 lightUsing 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

lightShirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue

Some further examples:

Object Colour of lightColour object seems to be

Red socks

Red Red

Blue Black

Green Black

Blue teddy

Red Black

Blue

Green

Green camel

Red

Blue

Green

Magenta book

Red

Blue

Green

Using filtersUsing filtersFilters can be used to “block” out different colours of

light:

Red Filte

r

Magenta

Filter

Investigating filtersInvestigating filters

Colour of filter Colours that could be “seen”

Red

Green

Blue

Cyan

Magenta

Yellow

ColorColor MixesMixes WellWell

http://www.explorelearning.com/index.cfm?method=cResource.dspResourcesForCourse&CourseID=332

Red

Magenta

White

Yellow

Blue Green

Cyan

RefractionRefraction

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