Light

- Overview of light

- Properties of light

- Luminous and non-luminous

objects

- History of light

- The electromagnetic spectrum

- Prisms

- Colour & Colour Blindness

Where does light come from?

The SUN!!

• The sun is a star located 1.50 x 108 km, or 1 Astronomical Unit, away from Earth. • It provides energy in the form of light through a process called nuclear fusion. • Nuclear fusion occurs when two atoms that naturally repelled each other are pulled together by a superior force and the atoms fuse together. • Nuclear fusion produces energy that reaches us as heat and light.

• The sun provides the energy that enables life on Earth.

What The Heck Is Light

Properties of Light

• Light travels in straight lines:

Laser

• Light travels VERY FAST – 3.0X108m/s

= 300,000 kilometres per second.

At this speed it can go around the world 7.5 times in one second.

The Strangeness of Light

• The speed of light (c) is constant

• Nothing moves faster than the speed of light

• Anything with mass cannot travel at the speed of light

• 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 reflectlight 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.

Shadows

Shadows are places where light is “blocked”:

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

Fun Science Light Video

History

• Unlike heat and sound energy which requires a medium (a physical substance) to move, light does not

• Light is transferred through radiation in a vacuum at the speed of light (3.0X108 m/s)

• Light is classified as an Electromagnetic Wave

Modern electromagnetic waves

• Today we have identified many types of electromagnetic waves which makes up our electromagnetic spectrum

The Electromagnetic Spectrum video

Modern View Continued

As we decrease wavelength, we increase frequency and energy

The Visible Light Spectrum

• Different colours have different wavelengths!

The Surprising Universe

• Today Scientists use different portions of the electromagnetic spectrum to collect and analyze data about stars and galaxies

• This provides them with completely different views compared with using visible light only

The Surprising Universe

Essential Knowledge, Skills, and Processes

• Analyze the effects of a prism on white light and describe why this occurs. Explain why a rainbow occurs.

Answer: Different

colours have different

wavelengths which

bend differently as

they pass through the

prism

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

Prisms

• What happens when you place two prisms next to each other?

Simulation

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

Colour Adding and Subtracting Simulation

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 pants 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 soccer uniform:

White

light

Shorts look blue

Shirt looks red

• In different colours of light this uniform would look different:

Red

lightShirt looks red, why?

Shorts look black, why?

Blue

light

Shirt looks black, why?

Shorts look blue, why?

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

Red Filter

Magenta Filter

Colour Blindness

• The tricky thing about colour blindness is that many people don’t know they are colour blind until they get tested

• (40% of colour blind pupils currently leaving secondary school are unaware that they are colour blind)

How many animals are

there?

6!

• Red Green Colour Blindness is caused by a gene on the X chromosome therefore, since males have 1 X and 1 Y while females carry 2 X’s, this issue is predominately found in males (7-10% of the overall population) and is very rarely seen in females.

• For these people, they cannot see red and green light.

• Blue Colour Blindness is equally unlikely for both males and females as the deficient gene is found on chromosome 7. These people can’t see blue colour light

• In both these cases the problem isn't as straight forward as not seeing blue, red or green light. If what they are looking at contains these colours, they will not be seen.

What is Colour Blindness

Light and Colour - Bill Nye Video