light present

What is light and why is it essential to life?

LIGHTLIGHT

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Light is a form of energy. It can be Light is a form of energy. It can be changed changed from one form of energy to from one form of energy to another.another.

For example, light entering your eye is changed to chemical and electrical energy which is transmitted to your brain.

Light energy can only be produced from other forms of energy.

What is light ?







Two types of light energy



Objects that convert their energy to produce their own light are said to be

LUMINOUSLUMINOUS.

For example, some For example, some fish living in the fish living in the depths of the ocean depths of the ocean produce their own produce their own light to attract prey.light to attract prey.

Two types of light energyTwo types of light energy

NON LUMINOUSNON LUMINOUS objects do not give off their own light, they reflect light.

For example you can see a car because it is reflecting light from the sun.



But how does light travel?

- Ocean waves travel on the surface of the water. You can see them and you can feel them.

- Have you ever seen a flag on a windy day? The wind creates waves in the flag.

- Sound is also a type of wave that we cannot see.

- Sound waves need something to travel through (like waves through the ocean or wind through a flag). Sound can travel through air because air is made of molecules. These molecules carry the sound waves by bumping into each other, like dominoes knocking each other over. Sound can travel through anything made of molecules - even water!

- There is no sound in space because there are no molecules there to transmit the sound waves.



All light has both particle-like and wave-like properties.

Light is made of discrete packets of energy called photons.photons.

Photons travel at the speed of light (300,000 km/s).



• White light is all colours, like the colours of the rainbow. • Sir Isaac Newton discovered the colour of light by shining white light through a prism. • This is called the "visible light spectrum."

So light is a form of energy?



- Light is energy and there is energy beyond visible light.

- The visible light spectrum is a part of a larger spectrum called the:

Electromagnetic SpectrumElectromagnetic Spectrum.

Light is energy

When you tune your radio, watch TV, send a text message, or pop popcorn in a microwave oven, you are using electromagnetic energy. You depend on this energy every hour of every day. Without it, the world you know could not exist.

Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion.

ELECTROMAGNETIC ENERGYELECTROMAGNETIC ENERGY







Our Sun is a source of energy across the full spectrum, and its electromagnetic radiation bombards our atmosphere constantly. However, the Earth's atmosphere protects us from exposure to a range of higher energy waves that can be harmful to life.

OUR PROTECTIVE ATMOSPHEREOUR PROTECTIVE ATMOSPHERE



Exposure to Gamma rays, x-rays, and some ultraviolet waves waves can alter atoms and molecules and cause damage to cells in organic matter.

These changes to cells can sometimes be helpful, as when radiation is used to kill cancer cells, and other times not, as when we get sunburned.



Beams of Light

Electromagnetic waves do not need molecules to travel, unlike sound waves.

Electromagnetic waves can travel through air and solid materials as well as empty space.

Light is an electromagnetic wave we can see.

This is why astronauts on spacewalks use radios to communicate. Radio waves are one kind of electromagnetic wave.

Rays of Light & reflections

A stream of light rays is called a ray of light.a ray of light.

Light can pass through some materials and it can also be reflected by other materials.

TRANSPARENT OBJECT

Glass, clear water, clear plastic cling

wrap.

TRANSLUCENT OBJECT

Frosted glass or stained glass

windows.

OPAQUE OBJECT

Wood, cement, concrete

What is a shadow?

A shadow outlines the area where light cannot A shadow outlines the area where light cannot reach.reach.

There are two types of shadows.There are two types of shadows.

UMBRA SHADOWThis is a complete shadow. Think of using a torch to make animal shadows on a wall.

PENUMBRA SHADOWThis is a semi shadow with usually a fuzzy outline.

WAVESTOWNWAVESTOWN







This Doppler-radar image seen on TV weather news uses microwaves for local weather forecasting.

Infra-red Thermal Imaging







Gamma Rays!!

Reflections & Plane Mirrors

One property of light is that it reflects off surfaces.When you look at yourself in a plane mirror you see an image of yourself.

Plane mirrors produce virtual, upright images that are the same size as the

object and the same distance from the surface of the mirror.

The reflection in the mirror appears to originate from inside the mirror at a distance equal to the distance the person is in front of the mirror.

The law of reflectionWhen a ray of light strikes a plane mirror, the light ray reflects off the mirror. Reflection involves a change in direction of the light ray.

light present

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