Light

1) Properties of light2) Reflection3) Colors4) Refraction

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:

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 summary

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 - ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

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 !

!!

Image - is a position in space where all the reflected light appears to diverge from.

Images formed by plane mirrors are virtual

1.The image formed by a plane mirror is Virtual Image– not real therefore can not be caught

on a screen– Images are formed in locations where

light does not actually reach– Rays do not actually cross at the point

behind the mirror. • They only appear to have originated

there.

2.The object distance (often represented by the symbol do) is equal to the image distance (often represented by the symbol di).

3.Dimensions of the image are the same as the dimensions of the object .

4. The image is upright 5. Left right reversal – The image is

laterally reversed.

Specular 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

Reflection off of smooth surfaces such as mirrors or a calm body of water leads to a type of reflection known as specular reflection. Reflection off of rough surfaces such as clothing, paper, and the asphalt roadway leads to a type of reflection known as diffuse reflection.

Color

White light is not a single color; it is made up of a mixture of the seven colors 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 colors of the rainbow:

RedOrangeYellowGreenBlue

IndigoViolet

Adding colorsWhite light can be split up to make separate

colors. These colours can be added together again.

The primary colors 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 colorThe color an object appears depends on the

colors of light it reflects.

For example, a red book only reflects red light:

White

lightOnly 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 colored light

If we look at a colored object in colored 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

airglass

Refraction is the bending of light

when the light passes from one medium to another.

airglass

Useful words to describe refraction of light

normal

incident ray

angle of refraction

angle of incidence

refracted ray

Examples of refraction of light

Bent chopstick

• The chopstick appears bent because of refraction

The bending occurs because the speed in which light travels through a substance depends on the substance's density. In air light travels at about 186,000 miles per second but in water light travels only about 140,000 miles per second (see chart below). Since light travels slower in water than in air, water is said to have a greater optical density than air.

‘When hunting a fish under water, you should aim your spear directly at the fish.’

Do you agree?

Yes, of course.

No, because the fish is actually located somewhere else.

No, because size of objects changes when they are put under water.

“The Inverse Square Law”

The Energy we receive is inversely proportional to the square of the distance.

Diffraction

Diffraction is the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

Only transverse waves

may become

polarized.

POLARIZATION

•Sun glasses reduce the glare of bright light using the phenomenon of polarization