Light Everything You need To Know About Light

7/29/2019 Light Everything You need To Know About Light

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Lightby: MARILYN C. SANTOS

Santa Rosa Science and Technology High School



Welcome to a power point

presentation on LIGHT.

• We will study the following:

• 1. What is light?

• 2. What is the source of light?• 3. What makes up the visible spectrum?

• 4. How does a prism work?

• 5. What are the properties andcharacteristics of light?



A light review:

• Our primary source of light is the sun.• Light travels in straight lines at a speed of

186,000miles per second.

• Light waves travel faster than sound waves.

• Light energy from the sun travels throughspace , reaches earth, and some of it turns toheat energy and warms the earth’s air.

• Light from the sun also travels to the cells of green plants (producers) and is stored asenergy.

• When light reaches an object, it is absorbed,reflected, or passes through it.



Discovery of Light

• Isaac Newtonlight behaves like a particle

• Alfred Huygens

light behaves like a wave• Max Planck

Dual Nature of Light – can be a particle

or a wave• James Clark Maxwell

discovered the Electromagnetic Theory

of Light



Sensing Light

• Humans have two

light detectors.

• Do you know what

they are called?

Did you realize cameras and camcorders are light detectors too?



Where does light come from?

Our major light source:

the Sun



Where else does light come from?



Sorting light sources

Natural vs. Man-made (artificial)



Are these light sources?

moon

water mirror

These items are not light sources, instead they

are reflecting light from other sources.



How does light travel?

Light rays travel in straight lines from the light source.

When it hits an opaque object, some light is absorbed andthe rest reflects off.

If the object is transparent, light rays pass through iteasily.

If the object is translucent, some light can pass through,

but the rest of the light will be reflected.

light

source



Vocabulary

• Transparent: materials that allow alllight to pass through

• Translucent: letting light pass through

but scattering it• Opaque: materials that do not let light

pass through

• Transmit: to send (as in sound or light).It also means light passing through an

object.



How do we see?

Light coming from, (or reflecting off) objects enters the eye through the corneathen the pupil.

It is focused clearly by the lens on to theretina.

The light sensitive cells of the retina gather

information about patterns of light and dark,colour and movement and send it through theoptic nerve.



How do we see?

Information entering the brain through theoptic nerve, is then transmitted throughmore nerve pathways to the visual cortex.

Here the patterns of light and dark, colour

and movement are interpreted.

The brain, based on past experience, canthen understand what it ‘sees’.



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 smokefirst 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

-The Sun

- Lamps

- Lights- Lasers

- Campfires

-The Moon

- Mirrors

- People

- Objects



• Shadows

Shadows are places where light is “blocked”:

Rays of light



How does light form shadows?

Light rays travel in straight lines, radiating out from thelight source.

If rays are blocked by an opaque object a shadow formswhere the light cannot reach.

If the light source is moved closer to the object, more

light is blocked and a larger shadow is formed.

lightsource

lightsource



Out of the Darkness

-If the light source is small compared to the size of the object, thenthe shadow will be SHARP

-If the light source is of comparable size to the object, then the

shadow will be “fuzzy”. The dark inner region is called the UMBRA;

the grey region is called the PENUMBRA.



How does sunlight cause shadows?

6am

8am

9am

12pm

2pm 10am

3pm

4pm

7pm

Looking North,

the Sun appears to rise in theEast...

...and travelacross the skyuntil it sets in the

West.

The position of theSun effects theposition and length ofthe shadows created.

Thanks to thisnatural phenomenon asundial is able to tellus the time, as long as it is a sunny day!



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



How does light reflect?

Angle of incidence

Angle of reflection

The ‘angle ofreflection’ isalways equalto the ‘angleof incidence’.



• The Law of Reflection

Angle of incidence = Angle of reflection

In other words, light gets reflected from a surface at THE

SAME ANGLE it hits it.

The same !!!



Light can only be reflectedin straight lines.



Clear vs. Diffuse Reflection

• Smooth, shiny

surfaces have a clear

reflection:

Rough, dull surfaces have a diffuse

reflection.

Diffuse reflection is when light is scatteredin different directions



How do we see colour?light

source

Light from most lightsources looks white, butactually contains all thecolours of the spectrum;also known as the

rainbow.

If an object looks blue, itis absorbing every colourexcept blue, which isreflecting off it andentering your eyes.

If an object looks orange,

it is absorbing every colourexcept orange, which,again, is reflecting off andentering your eyes.

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



Colour

• White light is not a single colour; it ismade up of a mixture of the seven

colours of the r ainbow.

We can demonstrate this bysplitting white light with aprism:

This is how rainbows areformed: sunlight is “split up” by raindrops.



The colours of the rainbow:

• Red

• Orange

• Yellow

• Green• Blue

• Indigo

• Violet

Remember: Roy G. Biv !!!



Wavelengths of Light

• Red Light – l = 680 nm

• Green Light -l = 500

nm

• Blue Light - l = 470 nm



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



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, in addition to being ugly, would reflect

purple light

(or 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 the

outfit below – I mean, from a physicsstandpoint, not as a fashion choice:

White

light

Shorts look blue

Shirt looks red



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

Red

light

Shirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue



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

RedFilter

MagentaFilter



Some common optical tools having lenses,mirrors, and/or prisms in it.

– eyeglasses

– flashlights

– cameras – binoculars

– microscopes



• Eyeglasses: have lenses

c. Hyperopia (farsightedness)

a. Normal eye

b. Myopia (nearsightedness) Corrected with concave lens

Corrected with convex lens

No correction needed



• Flashlight: has lenses and a mirror



• Cameras: have lenses, mirrors, and a

prism



• Binoculars: have lenses and prisms



• Microscope: has lenses



• Explain the terms transparent, translucent,

and opaque, and give an example of each.

Plastic wrap Wax paper Aluminum Foil

Transparent Translucent Opaque

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Contributions of some scientists in creating

and using optical tools:

– Galileo Galilei

– Robert Hooke – Anton van Leeuwenhoek

– Isaac Newton



Galileo Galilei

• Italian

• Lived from 1564-1642

• Developed the refracting telescope

• Developed the first known example of the

microscope

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Robert Hooke

• English


• Devised the compound microscope and

illumination system

• Discovered plant cells

• Examined fossils with a microscope

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Anton van Leeuwenhoek

• Dutch; born in Holland

• Lived 1632-1723

• Made over 500 simple microscopes

• Discovered bacteria, free-living and

parasitic microscopic protists

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Isaac Newton

• English


• Discovered that white light was not a

simple entity, but splits into a range of colors

• When he passed white light through a

glass prism, he noted that a spectrum of light was formed; particle theory of light

• Reflecting telescope

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Now explain to your partner:

What is thedifference betweenlight from the Sunand light from themoon?

Why does the

Sun rise inthe East andset in theWest?

Why does an

orange look adifferent colourto a banana?

How does aperiscopework?

Why can’t wesee anythingwithout alight source?

Documents

Light Everything You need To Know About Light