Light and Optics

1.0 Our knowledge about light and vision comes from explanations, inventions, and investigations.1.1 – The Challenge of Light

Throughout time people have explored the properties of light. Through trial and error scientists have come up with some definite properties of light:

Light travels in a straight line. Light can be reflected. Light can change direction. Light is a form of energy.

1.2 – Optical Devices An optical device is any technology that uses light. Some examples include: eye glasses, microscopes, telescopes, binoculars.

MicroscopesThe invention of the microscope has opened up our understanding of a world of microorganisms that affects our lives significantly. A Dutch scientist by the name of Antonie van Leeuwenhoek was one of the first to make these discoveries with a microscope of his own design. This world of microorganisms is so vast that there is a branch of scientific study devoted entirely to them. It is called microbiology.

Telescopes1

Telescopes work much the same as a microscope. They both collect and magnify light. Galileo was not the inventor of telescopes but he did make many of his own and was the first to make astronomical discoveries. There are two basic types of telescopes: reflecting telescope and refracting telescope.

1. The refracting telescope uses a combination of lenses. The larger one gathers light and focuses the rays towards the objective lens.

2. The reflecting telescope has a large mirror at one end that gathers light very well and reflects it off another smaller mirror into the objective lens.

2.0 – Light behaves in predictable ways 2

2.1 – Light Travels in Rays and Interacts with Material Ray DiagramsAs light leaves a source it travels in a straight line. Scientists use ray diagrams to show how light travels. Here is a simple ray diagram with a flash light shinning into someone’s eye.

So the farther we move away from the light source fewer rays actually reach our eye. That is why light is brighter to us (or more intense) when it is close and not as bright (or less intense) when we are farther away.

Light Interacts with Different Materials

If the material is transparent the light will travel right through it. We are able to see the object on the other side perfectly. If it is translucent some of the light will pass through but not all of it. You would be able to see outlines of an object on the other side but not very many details. A material that is opaque will not allow any light to pass through it. So you cannot see any object through this material.

Luminous – An object that produces light (sun, lamp).Non-luminous – An object that does not produce light.How do we actually see things?

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Types of Reflection1. Regular reflection occurs when light hits a smooth surface.

Regular reflection produces a clear image because the reflected rays remain parallel.

2. Diffuse reflection occurs when light hits an uneven surface.

Because the surface is uneven the reflected rays do not remain parallel. The image is not visible.

2.2 – The Law of Reflection When an incoming light ray (incident ray) bounces off a reflective surface it bounces off at the same angle it comes in at.

According to the law of reflection, the angle of incidence equals the angle of reflection.

Check and Reflect #1 – Light and Optical Systems (2.1 and 2.2)4

1. Why is the light brighter (more intense) when it is closer to our eyes? _________________________________________________

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2. What is the difference between the terms transparent, translucent, and opaque? ___________________________________________

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3. Give an example of something that is luminous and non-luminous. ______________________________________________________

4. What is the difference between regular and diffuse reflection? ________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. Use a diagram and explain what the law of reflection means.

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2.3 – Reflecting Light with Curved Mirrors 5

We have discussed flat mirrors and how they relate to the law of reflection. Now let’s discuss curved mirrors. There are two basic types of curved mirrors: concave and convex.

A concave mirror has a surface that curves inward like a satellite dish. These types of mirrors collect light. All of these reflected rays of light will head to a common position called the focal point.

examples:

Concave Mirror Images – Activity pg 198 in textUse the following space to produce a table for all of your observations from this activity.Close up

Some distance

Far away

Conclusion: ____________________________________________________________________________________________________________________________________________________________________A convex mirror has a surface that curves outward. Because they curve outward they are actually spreading the light rays out.

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examples:

Curved mirrors also obey the law of reflection. But because the rays of light are hitting the mirror at slightly different angles (angle of incidence), they will reflect at slightly different angles (angle of reflection).

Check and Reflect #2 – Light and Optical Systems (2.3)

1. Use two diagrams to show how concave and convex mirrors obey the law of reflection.

2. How do objects appear in a concave mirror when they are close to the mirror and far away from the mirror? _____________________

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3. What is a focal point? ____________________________________________________________________________________________

4. Give two examples of convex mirrors and two examples of concave mirrors. _________________________________________________

2.4 – Transparent Substances Refract Light

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When you look at an object in a medium (lets talk about water for example) we are actually seeing the refracted image not the actual image. Refraction is when light bends a it hits different substance.For example, trying to catch a fish in a tak of water. This is tricky because the image we are seeing is actually the rfrated image of the fish and not the actual fish.

Refraction is due to changes in the speed of light. As light goes through a more dense substance there are more particles to get in the way. This causes the light to slow down. This slowing down is what causes the light to bend or refract.

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2.5 – Lenses Refract and Focus Light A lens is basically a transparent, curved material, like glass. It should be smooth and regularly shaped. Lenses refract light in predictable ways depending on its material, thickness and shape. The most useful lenses are obviously those that form an image when the rays of light are refracted through them.

A concave lens is thinner in the center than on the edges. As light passes through this kind of lens it is refracted outwards / they are spread out. These light rays will never meet on the other side of the lens.

Convex lenses are thicker in the middle than on the outside. As light passes through this kind of lens it is refracted inwards / they move towards one another. These light rays will meet at the focal point on the other side of the lens.

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A convex lens is a light collector just like a concave mirror. A refracting microscope uses convex lenses. A convex lens can also form a real image, which can be projected onto a screen. The only consideration to make with a convex lens is that the image that is formed is upside down.

Convex and Concave Lens Investigation

Problem – Will the distance an object is from the lens affect how we see it?Hypothesis - _____________________________________________________________________________________________________________________________________________________________________________________________________________________________

VariablesManipulated - __________________________________________Responding - ___________________________________________Controlled - ____________________________________________

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Procedures - _______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Materials - ___________________________________________________________________________________________________________

Observations10

Concave Lens – How Images Look from Different Distances

Very Close Close

Far Very Far

Convex Lens – How Images Look from Different Distances

Very Close Close

Far Very Far

Discussion

1. Which type of lens creates a focal point? ____________________2. How do you know a focal point is created? ___________________

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Conclusion

1. Restate your hypothesis in past tense. ____________________________________________________________________________________________________________

2. Was your hypothesis correct or not? ______________________________________________________

3. How do you know your hypothesis is correct or not? __________________________________________________________________________________________________________________________________________________________________

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Check and Reflect #3 – Light and Optical Systems (2.4 – 2.5)1. What is refraction? Include a diagram to show how light is

travelling. _____________________________________________________________________________________________________

2. Use the word density or particles to explain why refraction happens. ______________________________________________

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3. What are two differences between concave and convex lenses?________________________________________________________________________________________________________________________________________________________________________

4. How does the image change as light passes through a concave lens at a very close and very far away position? ________________________________________________________________________________________________________________________________________________________________________________________________________________________

5. How does the image change as light passes through a convex lens at a very close and very far away position? ________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Section 2 Assignment – Light and Optical SystemsChoose questions that together total 12 marks.

Use complete sentences to answer these questions in your bound booklet.

1. How did Anton van Leeuwenhoek and Galileo make contributions to science. /2

2. Use a diagram and explain why a light is more intense when it is closer to your face. /2

3. What is the difference between transparent, translucent and opaque. Give an example of each one. /3

4. Use diagrams and explain the difference between regular and diffuse reflection. /2

5. What is the law of reflection? Use a diagram in your answer. /2

6. Draw ray diagrams that show how light reflects off of a concave mirror and convex mirror. Remember the focal point. /3

7. Draw ray diagrams that show how light passes through a concave lens and a convex lens. Remember the focal point. /3

8. What are two examples of a convex mirror? /1

9. Use the word density or particles to explain why light refracts. /2

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3.0 – Light is part of the electromagnetic spectrum and travels in waves.

3.1 – The Wave Model of Light

Properties of Waves

Regardless of the type of wave (sound, water, light, electromagnetic) we are discussing they all have similar properties.

What is a:Wavelength? ________________________________________________________________________________________________________Amplitude? __________________________________________________________________________________________________________Frequency? __________________________________________________________________________________________________________Crest? ____________________________________________________

For waves that have the same amplitude, the greater the frequency the more energy output there is. The greater the frequency the more crests there will be in a certain amount of time.

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Light Waves

White light is made up of all the colours of the rainbow. These colours make up the visible light spectrum. What are the colours? What order are they in?

As light passes through a prism or raindrops the white light rays are refracted and separate into “the colours of the rainbow”.

Each colour of light is refracted at a slightly different angle. This is because each colour has a slightly different wavelength.

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3.2 – Electromagnetic Spectrum There is another world of energy that goes unnoticed every day. Visible light only makes up a small portion of electromagnetic radiation. These other forms of energy, that also move in waves, include radio waves, microwaves, infrared waves, ultraviolet light, x-rays and gamma rays.

For each of the following examples of electromagnetic radiation identify the wavelength and what purposes it has in our lives.

Radio Waves____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Microwaves____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Infrared Waves____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Ultraviolet Light__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

X-rays__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Gamma Rays__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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3.3 – Producing Visible Light An incandescent light bulb is the most common type of artificial light. It consists of a very fine filament in connecting two sides of a circuit. As electricity passes through the filament it lights up instantly. Most of the energy is given off as heat. Only 5% of that energy is actually given off as light. This makes the incandescent light bulb a very inefficient light source but quite a good heat source.

Fluorescent light bulbs work a little differently. Fluorescent bulbs consist of two electrical prongs at both ends, a glass covering, mercury gas to fill the tube and a white powder, called phosphor, that covers the inside of the glass. As electricity passes into the tube it energizes the gas causing it to give off ultraviolet radiation. The radiation contacts the phosphor causing it to glow, giving off white light.

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filament

Chemiluminescent light is similar to fluorescent light. However, the material that is in these lights has the ability to store the radiation. This allows these light sources to produce light long after the source of radiation has stopped. Some examples of these types of light are glow in the dark necklaces and stars.

Bioluminescence is when living things give off light from their bodies. This involves a chemical reaction between materials in the organism’s body. With the angler fish the “lure” is filled with bacteria that are actually the ones that are bioluminescent. The fire fly actually has an organ in its body called the photophore where this chemical reaction occurs that produces light.

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3.4 – The Colours of Light

We can use various objects to split white light into all the colours of the visible light spectrum. You can also combine these colours to produce white light again. Actually all you really need is the colours red, green and blue. These three colours are the primary colours. Combining these colours produces the secondary colours: magenta yellow and cyan.

Check and Reflect #4 – Light and Optical Systems (Sections 3.1-3.4)

1. Using words and a diagram, explain what a wavelength is. ____________________________________________________________________________________________________________

2. What is white light? _____________________________________________________________________________________________________________________________________________________

3. Why can we see the colours that make up the visible light spectrum? _____________________________________________

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4. How does wavelength determine the energy level that is given off in the form of waves? ____________________________________

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5. Pick three examples from the electromagnetic spectrum and describe how each benefits our lives. _______________________

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6. Describe how incandescent and fluorescent light bulbs differ.________________________________________________________________________________________________________________________________________________________________________

7. What is the efficiency of those two bulbs as light sources? ________________________________________________________

8. How do organisms give off light? ___________________________________________________________________________________________________________________________________________

9. What are the primary and secondary colours? _________________________________________________________________________

10. What colours would you need to combine to create white light again? _______________________________________________

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Section 3 Assignment – Light and Optical SystemsAnswer all of these questions in your bound booklet.

1. Finish the following sentences: a) As the frequency of waves increases the amount of energy ______. b) Increasing wavelength ____________ frequency. /2

2. What is white light? /1

3. What are the colours that make up the visible light spectrum? List them in the correct order. /1

4. Why does white light create a rainbow when it passes through a prism? /2

5. What is the wavelength range of visible light? /1

6. Describe the difference between incandescent, fluorescent and phosphorescent light. /3

7. How does a firefly give off light? /1

8. What are the primary colours? /1

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4.0 – Eyes / cameras capture images using the properties of light. 4.1 – Image Formation in Eyes and Cameras

Use the following three diagrams to help explain how eyes and cameras allow light inside to form an image.

Light enters the eye through a hole called the pupil. The size of the pupil is controlled by a band of muscle that is called the iris. This is the part of the eye that is coloured. As the light passes through the pupil it hits the lens. The lens refracts the light as necessary and then continues on until it hits the retina. The retina is covered with specialized cells called cones and rods. Cones are sensitive to colours and rods are sensitive to light. These two photoreceptors pass on their messages to the brain through our optic nerve. Our brain then interprets these messages as images. Muscles attached to the lens of the eye relax or contract to change the shape of the lens. This allows you to focus the object onto the retina of the eye.

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Cameras work in a similar way. Light passes into the camera through a hole called the aperture. The size of the aperture is controlled by the diaphragm. The light is also refracted as necessary by the lens of the camera. The light continues on until it hits the film. An image is imprinted onto the film which is then turned into actual pictures. A camera moves the lens closer or farther away from the object in order to focus the image on the film of the camera.

NearsightednessWhen a person is nearsighted the focal point of the image occurs before the retina. Therefore the image will not be focused. To correct this problem people often are fitted with concave lenses.

FarsightednessWhen a person is farsighted the focal point of the image occurs after the retina. Therefore the image will not be focused. To correct this problem people often are fitted with convex lenses.

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4.2 – Other Eyes in the Animal Kingdom

Two types of eyes are Camera Eyes and Compound Eyes.

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Camera EyesThese types of eyes consist mainly of a cornea, lens, retina and are generally round in shape. Some organisms that have camera eyes include: humans, fish, cats, birds

Compound EyesThese eyes are made up of many smaller units called ommatidium. Organisms that have compound eyes include: insects and crustaceans (shrimp, lobster, crayfish).

Check and Reflect #5 – Light and Optic Systems (4.1-4.2)

1. Explain in detail how light enters our eyes and eventually forms an image in our brains. _____________________________________

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2. Match up the parts of our eyes and parts of a camera that have similar functions. You should have four matches at least.

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3. How do our eyes focus on an image? ________________________________________________________________________________________________________________________________________

4. How do cameras focus on an image? ________________________________________________________________________________________________________________________________________

5. What is the problem when people have nearsightedness? Farsightedness? How is this problem fixed? __________________

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Section 4 Assignment – Light and Optical SystemsAnswer both of these questions in your bound booklet.

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1. Use the following terms to explain how we let light into our eyes to form an image: cornea, pupil, iris, lens, rods, cones, retina, optic nerve, focal point and muscles. /10

2. What is the difference between farsightedness and nearsightedness? /2

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