How do we see things?How do we see things?•

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The Road to EnLIGHTenment The Road to EnLIGHTenment

Light & Geometric Optics Light & Geometric Optics

How do we see things?

• We see light

• Some objects make their own light (aka: luminous objects)

e.g. stars, light bulbs, televisions, etc…

• Some objects reflect light

(aka: non-luminous or reflective objects) e.g. planets, moons, trees, etc…

• We see light

• Some objects make their own light (aka: luminous objects)

e.g. stars, light bulbs, televisions, etc…

• Some objects reflect light

(aka: non-luminous or reflective objects) e.g. planets, moons, trees, etc…

What is Light?

• Light is a form of radiation, or energy, that is transmitted from one place to another by electromagnetic waves

• A ray of light travels in straight lines (In science terms: linear propagation)

• How do we know? Think about sunlight falling on a solid object, and the shadow that appears on the ground. Does it have fuzzy or sharp edges?

Which could be explained by light traveling in a straight line?

• Light is a form of radiation, or energy, that is transmitted from one place to another by electromagnetic waves

• A ray of light travels in straight lines (In science terms: linear propagation)

• How do we know? Think about sunlight falling on a solid object, and the shadow that appears on the ground. Does it have fuzzy or sharp edges?

Which could be explained by light traveling in a straight line?

Beams and rays Beams and rays

• Sometimes, if there is dust in the air, we see

“rays” of sunlight streaming into the room.

• A light “ray” is defined as a path taken by light energy

• A light “beam” is many parallel light rays

• Light rays do not interact with each other

• A light ray continues forever unless it has an interaction with matter that causes the ray to change direction or to be absorbed

• Sometimes, if there is dust in the air, we see

“rays” of sunlight streaming into the room.

• A light “ray” is defined as a path taken by light energy

• A light “beam” is many parallel light rays

• Light rays do not interact with each other

• A light ray continues forever unless it has an interaction with matter that causes the ray to change direction or to be absorbed

Light and matter Light and matter

• Light has four different ways in which it can interact with matter.

• At an interface between two media, light can be reflected or refracted

• Within a medium, light can be scattered or absorbed.

• Light has four different ways in which it can interact with matter.

• At an interface between two media, light can be reflected or refracted

• Within a medium, light can be scattered or absorbed.

“Seeing” Light

• “Visible light” is light the human eye can detect. It is only a small fraction of the electromagnetic spectrum which includes many things we would not call “light”, such as radio waves, microwaves, etc.

• The electromagnetic spectrum is the FULL range of radiation (energy emitted as waves)

• “Visible light” is light the human eye can detect. It is only a small fraction of the electromagnetic spectrum which includes many things we would not call “light”, such as radio waves, microwaves, etc.

• The electromagnetic spectrum is the FULL range of radiation (energy emitted as waves)

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Waves? Like in the ocean?

• Waves pass energy from one point to another as they rise and fall

• Highest point in wave = crest

• Lowest point in wave = trough

• Wavelength: distance from crest to crest, or trough to trough

• Frequency: the rate of repetition of a wave (how many times does the wave pass a set point in a period of time)

• The higher the frequency, the more energy a wave passes

• Waves pass energy from one point to another as they rise and fall

• Highest point in wave = crest

• Lowest point in wave = trough

• Wavelength: distance from crest to crest, or trough to trough

• Frequency: the rate of repetition of a wave (how many times does the wave pass a set point in a period of time)

• The higher the frequency, the more energy a wave passes

Back to the Spectrum Back to the Spectrum

• Notice the pattern in the wave as it travels across the spectrum

• Radio waves have a longer wavelength, lower frequency, and are used to carry information around the world

• Gamma rays have a shorter wavelength, higher frequency, and can penetrate human tissues!

• The visible spectrum is right in the middle (notice blue is shorter than red)

• Notice the pattern in the wave as it travels across the spectrum

• Radio waves have a longer wavelength, lower frequency, and are used to carry information around the world

• Gamma rays have a shorter wavelength, higher frequency, and can penetrate human tissues!

• The visible spectrum is right in the middle (notice blue is shorter than red)

How do we get colours?

• When sunlight or white light is shone through a prism, light separates into the colours of the rainbow (ROYGBV)

• This range of different colours is called the visible spectrum

• When sunlight or white light is shone through a prism, light separates into the colours of the rainbow (ROYGBV)

• This range of different colours is called the visible spectrum

The Additive Colour Theory of Light

• White light is composed of different colours (wavelengths) of light

• It is possible to produce white light by combining only three colours!

• White light is composed of different colours (wavelengths) of light

• It is possible to produce white light by combining only three colours!

Subtractive Colour Theory Subtractive Colour Theory

• When light waves strike an object, some of the wavelengths reflect (bounce off the object)

• The colour you see when you look at an object depends on the wavelength it reflects

• Using subtractive colour theory, the colours that are absorbed by an object are ‘subtracted’ from the reflected light seen by the eye

• Black objects absorb all colours, where white reflects all colours

• Blue objects reflect blue, and absorb all other colours.

• When light waves strike an object, some of the wavelengths reflect (bounce off the object)

• The colour you see when you look at an object depends on the wavelength it reflects

• Using subtractive colour theory, the colours that are absorbed by an object are ‘subtracted’ from the reflected light seen by the eye

• Black objects absorb all colours, where white reflects all colours

• Blue objects reflect blue, and absorb all other colours.

AS SEEN ON TV!

• There are 1000’s of pixels in red, green and blue

• The strength of each produces an overall colour which your brain then interprets

• What’s actually there

• What you see

• There are 1000’s of pixels in red, green and blue

• The strength of each produces an overall colour which your brain then interprets

• What’s actually there

• What you see

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Something to think about:

1) What wavelengths are being absorbed by the red colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the red ones.

2) What wavelengths are being absorbed by the blue colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the blue ones.

3) What wavelengths are being absorbed by the green colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the green ones.

1) What wavelengths are being absorbed by the red colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the red ones.

2) What wavelengths are being absorbed by the blue colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the blue ones.

3) What wavelengths are being absorbed by the green colour? What wavelengths are being reflected?

All wavelengths are being absorbed except the green ones.

Something to think about:

4) What will happen if blue and orange are combined?

They are complementary colours, so the new colour will be brownish.

5) What will happen if purple and green are combined?

4) What will happen if blue and orange are combined?

5) What will happen if purple and green are combined?

Producing Visible Light Producing Visible Light

LIGHTING UP THE DEEP

• Bioluminescence is the ability of some plant or animals to produce light (by a chemical reaction)

• 90% of all sea creatures are bioluminescent!!

• They use it to attract prey, scare off predators, attract mates or camouflage LIGHTING UP THE DEEP

• Bioluminescence is the ability of some plant or animals to produce light (by a chemical reaction)

• 90% of all sea creatures are bioluminescent!!

• They use it to attract prey, scare off predators, attract mates or camouflage

SOURCES OF LIGHT SOURCES OF LIGHT

• Incandescent light is that is produced by an object, such as a metal, at a very high temperature

• light bulb with a filament, which emits light as a way to release some of its energy

• Extremely inefficient! Only 5% of the energy put into the bulb is converted to light, the rest is released as heat

• Incandescent light is that is produced by an object, such as a metal, at a very high temperature

• light bulb with a filament, which emits light as a way to release some of its energy

• Extremely inefficient! Only 5% of the energy put into the bulb is converted to light, the rest is released as heat

Sources of light cont…

• Fluorescent light is emitted by substances when exposed to electromagnetic radiation

• More efficient than incandescent, but still release up to 80% of energy as heat

• a fluorescent bulb is a glass tube filled with a small amount of gas, and the inside of the tube is coated with phosphor (a powder than glows when exposed to energized particles)

• When electricity passes through the bulb, it energizes the gas, which emits UV radiation

• This radiation hits the phosphor which glows to emit light

• Fluorescent light is emitted by substances when exposed to electromagnetic radiation

• More efficient than incandescent, but still release up to 80% of energy as heat

• a fluorescent bulb is a glass tube filled with a small amount of gas, and the inside of the tube is coated with phosphor (a powder than glows when exposed to energized particles)

• When electricity passes through the bulb, it energizes the gas, which emits UV radiation

• This radiation hits the phosphor which glows to emit light

Sources of light cont…

• Phosphorescence is the ability to store energy from a source of light and then emit it slowly over a long period

•Glow in the dark!

• Phosphorescence is the ability to store energy from a source of light and then emit it slowly over a long period

•Glow in the dark!

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Sources of light cont…

• Chemiluminescence is the light produced from a chemical reaction without a rise in temperature

•Glow sticks

•Luminol is used in crime scenes because it glows when it reacts with the iron found in blood!

• Chemiluminescence is the light produced from a chemical reaction without a rise in temperature

•Glow sticks

•Luminol is used in crime scenes because it glows when it reacts with the iron found in blood!

Sources of light cont…

• Tribloluminescence is the light produced from friction

• Some crystals can be made to glow by rubbing them together or crushing them

• Wint-o-green lifesavers… try biting one hard in a dark room with a mirror!

• Tribloluminescence is the light produced from friction

• Some crystals can be made to glow by rubbing them together or crushing them

• Wint-o-green lifesavers… try biting one hard in a dark room with a mirror!

Sources of light cont…

• Electric Discharge is a way of producing light by passing electricity through the air or another gas, such as neon

•Lightening

• Electric Discharge is a way of producing light by passing electricity through the air or another gas, such as neon

•Lightening

Sources of light cont…

• Electroluminescence is a way to transform electrical energy directly into light energy using a semiconductor

•LED’s (light emitting diode) use small amounts of electricity and do not contain delicate parts

• Electroluminescence is a way to transform electrical energy directly into light energy using a semiconductor

•LED’s (light emitting diode) use small amounts of electricity and do not contain delicate parts

Things to think about:

1. Why are nights brighter when there is snow on the ground?

2.What would happen if you used green light to try and grow plants? Why?

3. A girl buys a dress in a store with fluorescent lighting, and finds when she gets home that the dress is a slightly different colour than what she thought it was. Can you think of why this is?

1. Why are nights brighter when there is snow on the ground?

2.What would happen if you used green light to try and grow plants? Why?

3. A girl buys a dress in a store with fluorescent lighting, and finds when she gets home that the dress is a slightly different colour than what she thought it was. Can you think of why this is?

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1. a) List 3 types of radiation of the invisible spectrum that have wavelengths longer than visible light.

b) Name one application for each of these 3 types of radiation.

2. a) List 3 types of radiation of the invisible spectrum that have wavelengths shorter than visible light.

b) Name one application for each of these 3 types of radiation

3. Compare red light with blue light.

a) Which has the longer wavelength?

b) Which has the higher frequency?

4. a) are 2 ways in which radio waves and x-rays are similar and different?

5. A balloon appears yellow when seen in white light. Explain the colour it will appear in:

a) Green light b) Magenta light 6. What are 2 examples of natural light

and artificial light?

7. Why could light bulbs be called heat bulbs?

4. a) are 2 ways in which radio waves and x-rays are similar and different?

5. A balloon appears yellow when seen in white light. Explain the colour it will appear in:

a) Green light b) Magenta light 6. What are 2 examples of natural light

and artificial light?

7. Why could light bulbs be called heat bulbs?