Light

Light

Why is light important?

Light• We see things every day, from the

moment we get up in the morning until we go to sleep at night.

• We look at everything around us using light.

• Without light, you wouldn't see anything at all.

• There are two types of light: natural light or artificial light.

• Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

Lightning• Light travels faster than sound.• That is why the lightning is seen

before the thunder is heard.

Natural Light• The most important source of natural

light is the sun.• The sun gives the earth light and

energy.• The moon and stars receive light from

the sun and reflects it to the earth.• A firefly also produces light.

Artificial Light• Artificial light is light that is made

by people, or man-made.• This includes candles, kerosene

lamps, flashlights, and light bulbs.

Light• Light is a kind of energy that travels

in waves.• Light can pass through some things,

but not others.• Light travels very fast and in straight

lines.

Transparent• An object that lets all light pass

through it is called transparent.• These objects are transparent: clear

glass, eyeglasses, window, fish tank, clear plastics, and transparent tape.

Translucent• An object that lets some light pass

through it is called translucent.• These objects are translucent:

waxed paper, sunglasses, frosted glass, and thin fabrics.

Opaque• An object that lets no light pass

through it is called opaque.• These objects are opaque: rock,

metal, wood, fog, aluminum foil, thick paper, and brick.

Shadows• Shadows are caused

by opaque objects blocking the path of light.

• Long shadows are seen in early morning and late afternoon.

• Shorter shadows are seen at noon.

Reflections• Reflect is when light

or an image bounces back off an object’s surface.

• Light can bounce back off an opaque object.

• An image can bounce back off an object, such as, a mirror, pond or lake, or shiny metal.

More Reflections

How does light reflect?

Angle of incidence

Angle of reflection

The ‘angle of reflection’ is always equal to the ‘angel of incidence’.

on

off

• Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

• The Law of ReflectionThe Law of ReflectionAngle of incidence = Angle of reflectionAngle of incidence = Angle of reflection

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

The same !!!

Light can only be reflected in straight lines.

on

off

How do we see colour?light

source Light from most light

sources looks white, but actually contains all the colours of the spectrum; also known as the rainbow.

If an object looks blue, it is absorbing every colour except blue, which is reflecting off it and entering your eyes.

If an object looks orange, it is absorbing every colour except orange, which, again, is reflecting off and entering your eyes.

If an object looks red... (You get the idea!)

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

Spectrum of Color• When you look at a light, it appears to be white.• Light is made up of many colors. These

colors can be seen when light is broken up.• There are seven colors of light in a spectrum:

red, orange, yellow, green, blue, purple, and violet.

• These colors are always seen in the same order.

Rainbow• A rainbow appears in the

sky when the sun shines through droplets of water in the air, creating a spectrum of color.

• The white light is broken up into many colors.

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