Optics

We began class by reviewing applications of optics:
Stereoscopic Vision
    We are able to perceive our depth perception by the use of binocular vision. An object must be imaged by two cameras to view a 3D image as each of our eyes receives a different image, This can be done by the use of anaglyphs, color filter glasses and a head mount display. 
Microscope
     Microscopes use converging lenses to magnify objects too small for the eye to see. To obtain larger images two or more lenses are combined to make a simple compound microscope. 
Projector
     Two converging lenses in a projector refract light so that an object is uniformly illuminated. The object is placed a distance of one of two focal lengths in front of the projection lens, resulting in a large real image. 
Camera
     Light enters a camera lens system and strikes a plane mirror. Light is reflected up to the pentaprism where total internal reflection guides the light through the viewfinder. When the photograph is snapped the mirror lifts up and allows light to strike the film. 

     We then wrote our quizzes on ray diagrams and thin lens equations as well as discuss various eye prescriptions. If you have 20/20 vision, it means that when you stand 20 feet away from an object you see what the 'normal' person sees at 20 feet. Examples of prescriptions are -3.5, 7.1. 

      Notes:

Opticians prefer to use the optical power P of a lens instead of a focal length. Power is measured in diopters (D).

P= 1/f

f must be in meters to have P to be in Diopters. 

The optical power is positive for converging lens and negative for diverging lenses. The higher the optical power the shorter the focal length. 

Example

1. A nearsighted person can focus on objects no father than 20.0 cm from the eye. What power of a lens is needed to enable the eye to focus the eye on distant objects clearly?

First identify whether they need a converging or diverging lens. 

Diverging. Object is distant. 

do= infinity

f= ?

di= -20.0com

1/di+ 1/do = 1/f

1/-20 + 1/infinity =i/f 

= 0

The next person to go must be the quickest at saying the alphabet backwards. :)

Telescopes

We were given class time to finish the Thin-Lens Practise Problems. Here are the answers:

1. di= 36cm hi= -3.6cm
2. di= -15cm hi= 2.5cm
3. a)di= 510cm b)hi= -62.5
4. di= -30cm hi= 1.8cm
5. di=do= 5.0cm
6. di= -14cm f=4.7cm

The class was then given an assignment from the textbook; read pages 396-399, write two paragraphs summarizing telescopes and one type of telescope and draw the diagrams for each type of telesscope.
Telescopes
To view distant objects such the moon and stars with detail, two or more lenses must be used together. The images are smaller but since they are much closer they appear larger.
Galilean Telescope

This telecope uses both converging and diverging lenses. The image produced is virtual, upright and larger.
Reflecting Telescope
Refracting Telescope

This telescope uses two converging lenses. The image produced is virtual, inverted and larger.
Terrestrial Telescope
This telescope uses three converging lenses, the third lens located in the middle (erector lens) has the purpose of inverting the image so it is upright like the object. Images produced are virtual, upright and larger.
The next blog writer will be anybody who has not written and sits by the windows of the classroom

Thin Lens Equation

We started off Friday's class with Mr. Banow showing us how to derive the thin lens equation. Here is the link to the website: http://www.hirophysics.com/Anime/thinlenseq.html


The thin lens equation is:
1/di+1/do=1/f (which is exactly the same as the curved mirror equation)



M=hi/ho=-di/do

The sign rules are:
1. All distances are measured from the optical center
2. Distance of real images (behind the lens) are positive (virtual=negative)
3. Inverted=negative magnification, upright=positive

Examples:
1. A 8.0cm tall pencil is placed 17cm in front of a converging lens (with focal length of 10.0cm). How far and how tall will the image be?
ho=8.0cm
do=17cm
f=10.0cm
di=?
hi=?

1/di+1/do=1/f
1/di+1/17=1/10.0
1/di=1/10.0-1/17
di=24cm

hi/ho=-di/do
hi/8.0=-24/17
hi=-11cm

2. Where must a book be placed in front of a magnifying glass (converging, f=10.0cm), if a virtual image is to be formed 25cm in front of the lens? What is the magnification?
f=10.0cm
di=-25cm
do=?
M=?

1/di+1/do=1/f
1/-25+1/do=1/10.0
1/do=1/10.0-1/-25
do=7.1cm

M=-di/do
M=25/7.1
M=3.5x

http://www.youtube.com/watch?v=9pdEX4xtkLs

I don't know who is left to write the blog so whoever's last name comes first alphabetically of who is left can write it:)

Properties of Images

When the focal length is positive, the lens is converging. When the focal length is negative, the lens in diverging.

When stating the properties of an image there are generally four. Images are classified by their position, kind, attitude, and magnification.

Don't forget to draw your three lines when drawing a diagram!

Converging:

Distant: The image is behind the lens and at F. The image is real as well as inverted and smaller than the object.

Outside F`: The image is behind F and real. It is also the same size and flipped.

At F`: When there is an object at the focal length of a converging lens there is never an image.

Between F` and O: A virtual image that is in front of F will occur. The image is also larger then the object and upright.

Diverging:

Distant: The image is positioned in front of the lens at F. The image is also virtual as well as smaller than the original object. It remains upright when the light hits the lens.

Outside F, At F, Between F and O: The image is smaller, virtual, upright, and between F and O.

I pick.... jk i dont care who writes the next blog!

Converging and Diverging Lenses

At the beginnng of class we wrote a 10 question true and false quiz on the questions we inquired about that were presented and posted on the Wiki Page.

We then carried onto reviewing our sheets on what we learned in Tuesdays class; Contact Lenses, Eye Glasses, Artificial Lens, and Lasik Laser Eye Surgery.

As a class we inquired on several strange aspects of human eyes. We learned that when you die your pupils will in fact dilate because the muscles associated with your iris lose it's ability to control movement and becomes locked in a retracted state where the pupils appear to dilate. Then on Youtube we viewed a video of a man vibrating his eyes. Following that, we watched videos of a man who is capable of popping out his eyes by having strong control over his eye muscles.

We then took notes on Lenses - Converging and Diverging.

Lenses have curved surfaces or a very large number of flat surfaces located at slightly different angles

Converging/Convex Lense - (position lense) : thicker at the centre than at the edges

Diverging/Concave Lense - (negative lens) : thicker at the edges


After taking notes we analyzed a sheet of four different ray diagrams on converging and diverging lenses. By viewing these ray diagrams we were able to come up with three consistant rules that apply to every ray diagram:

1) The ray will go parallel and through F
2) The ray will go through F' and then parallel
3) The ray will go straight through O

Sorry I couldn't make it to class today Mr. Banow!! The next person to write a blog whoever who came latest to class... lol could be a few a options.

Correct Correction of Correct Correctness

...this title makes sense if you think about it.

In today's class, Mr. Banow set up four stations, each concerning a topic relating to eye correction:

• Contact Lenses
• Eye Glasses
• Artificial Lenses
• LASIK - Laser Eye Surgery

Contact Lenses

Contact Lenses are thin, transparent discs that sit on the cornea that can correct hyperopia (far-sightedness), myopia (near-sightedness), astigmatism, and presbyopia.

There are many different kinds of contact lenses, each with a different function. The six different types are daily-wear, extended-wear, disposable, colour-tinted, UV protection, and corneal reshaping.

Eye Glasses

Eye glasses are lenses that are attached to a frame. There are several different type of glasses:

• Corrective - changes the focal length in order to correct defects such as myopia or hyperopia

• Bifocal - allows for two different focal lengths so one can see near and far objects; the division is clearly visible

• Trifocal - similar to bifocal lenses, but with three different focal lengths

• Progressive - similar to bifocal, but the division is not visible as the lens is gradually changed

• Safety - used to protect the eye from physical damage

• Sunglasses - protects the eye from UV radiation

• Special - used for special functions, such as 3D red-cyan anaglyph glasses

Glasses are also made out of many different materials, such as crown glass, plastic, polycarbonate, Trivex, and high-index plastic. The material is chosen based on what the glasses are used for.

The lenses are either converging lenses (to treat myopia) or diverging lenses (to treat hyperopia).

The different types of lenses.

Artificial Lenses

Artificial lenses are replacement lenses for your eye. The two types are intraocular lens (IOL) and Crystalens. The Crystalens is considered to be superior because it can be manipulated by the ciliary muscles, but it costs more and requires a more intensive surgery.

LASIK - Laser Eye Surgery

LASIK is a medical surgery used to correct hyperopia, myopia, and astigmatism. A laser is pulsed on an exposed cornea, removing corneal tissue, therefore, reshaping it.

Procedure of LASIK:

1. Make an incision in the cornea to make a flap
2. Fold the flap back to expose the cornea
3. A laser is pulsed at the exposed cornea
4. The flap is replaced and any wrinkles or bubbles are smoothed

The surgery itself will only take a few minutes. The cornea will naturally seal back into place in a few hours and will completely heal in a matter of days.


At the end of class, we were instructed to watch a video from the Mythbusters Pirate Special. It can be found here if you have not already seen it.

The next blog will be written by whoever can figure out the title first!

Eye Projects

We started class by talking about our presentations and what we have to do, after that we moved on to Mr. Banow talking about how to make a wiki page. Following that we went to the computer lab for about 50 minutes to work on the projects.

And that is literally all we did that class, so not much to write about.. But there ya go :)

Vision, eyes.. and other stuff

In the begging of class we reviewed the last blog post (as usual)

and then started with a quiz that was based on the sheet we were given last class. (the human eye)

Next we also reviewed over our Animal vision booklets we had received the previous class.

Then we began all of the presentations on Eye Defects, where everyone was given a topic to research on eye defects and make a presentation about.

We learned a lot in the presentations:

Amblyopia (lazy eyes): the lack of

perfect vision.

usually blur vision in the effected eye. one eye or even both eyes wander to different spots and blur the vision. most patients don't notice the difference in vision but some people notice the eyes wondering to different

things in the room.

Treatments: patching the good eye or instilling tropical atropine in the eye for better vision.

Cataracts: A clouding that develops

in the lens of the eye. this can be caused by aging, ultra violet light, diseases (such as: diabetes) and others.

Treatments:

eye surgeries ECCE and ICCE

wearing sunglasses

and more

Myopia: near sightedness,

where the eyeball is longer that it normally should be which effects

the way light enters the eye.

can be caused hereditary.

Treatment:

corrective lenses

laser eye surgery

Colour Blindness:

inability to distinguish betweencertain colours, is

more common in men because it is effected by the X gene if it is damaged which would be more common in males. can be hereditary.

Treatments:

corrective lenses

contact lenses

Astigmatism:

when the cornea is abnormally curved and you cannot see properly. common in people who are near sighted.

Treatments:

corrective lenses

laser surgery

To end class Mr.B suggested another assignment involving presentations

Wiki Link

https://mrbanow.wikispaces.com/

Follow this to get to the Wiki for the Optics Applications assignment.

Optics

We started a new unit on optics last week and then were given a handout on the human eye. It included a labelled diagram that I have here:

Not sure why it's sideways..

Some important information that we took away from that handout was that:

1. The cornea causes light to bend (refract) at the surface of the eye.

2.The lens, whose shape or curvature, is controlled by the ciliary muscles and suspensory ligament, causes light to undergo even more refraction. The lens of the eye focuses light.

3. The iris located behind the aqueous humour and in front of the lens contracts or expands to change the size of the pupil. The size of the pupil is altered to let in different amounts of light.

4. The vitreous humour helps maintain the shape of the eye.

5. The white surface of the eye is called the sclerotic (sclera).

6. The retina is located at the back of the eye. It is light sensitive. The surface of the retina is where the lens focuses images to be transmitted to the brain. The retina contains different types of light-sensitive receptors called rods and cones. Rods are sensitive to dim light and do not respond to colour. Cones are sensitive to bright light and colour.

As an interesting note, all people have a dominant eye. The second eye is mainly used for depth perception.

After that we found our near point as well as our blind spot. The near point of an eye us the closest an object can be to your eye and still be clearly focused. For the average adult eye it is 25 cm although when we did ours as a class most people got numbers around 5-12 cm. The blind spot is located at the back of the eye near the optic nerve. There are no receptors located here which means that we cannot see anything on that spot.

I believe it was Thursday when we watched the cow eye dissection and if anyone is still interested in Katie's crazy antics, I have the link for the site. http://www.exploratorium.edu/learning_studio/cow_eye/

 The next handout we received was one on animal vision. We learned that dogs have a visual field of 240, and humans only have a visual field of 200 which means dogs are able to see a more broad image. This is because their eyes are located on the sides of their head and humans eyes are located on the front of their heads. Dogs cannot distinguish colours like we can because they only have 20% the photoreceptors we do. That means they can only see a limited colour spectrum.

Dogs also have a hard time seeing fine detail. The objects need to be large in order for them to see them otherwise it is all a blur to them.

Today we worked on our power point presentations which we will be showing the class tomorrow.

I don't know what's going on with the people and blogs, so..nobody has to write one ever again.
Jk Mr.Bananow, you can pick.

Application's of the Critical Angle and the Total Internal Reflection

On Monday's class we had a substitute and we reviewed what we did in the previous class and finished answering the example questions about critical ang

le, ---> --->

Critical angle is the measure of the angle of incidence when the angle of refraction is at 90 degrees. Once the angle of incidence is greater than the critical angle, total internal reflection will occur.

Then we were assigned to read pages 344-349 "Applications of the Critical Angle and the Total Internal Reflection", then you had to choose two of the applications you read and had to summarize each of them. The applications were :

Mirrors and Prisms- When light reflects off a mirror, about 10% of the light is lost. For good periscopes or binoculars have glass prisms that use total internal reflection. Almost no light is lost.

Fiber Optics- the light ray's enter the glass fiber and strikes the inside surface at an angle greater than the critical angle. The result is total internal reflection and so light bounce off the surface and keeps travelling through the fiber glass.

Sparkling Diamond- when light strikes the top surface of a diamond some light is reflected and some passes into the diamond and is refracted.

Twinkling and Shimmering- when stars seem to twinkle in the sky, it's not what it seems. when light is given off by the star's, the light enters the atmosphere and is refracted as it moves from one mass of air to another, and since the variable masses of air are in motion the star's seem to twinkle.

Mirages- there are two types of mirages inferior and superior. Inferior is when you are driving on a hot day and it seem's that there is water up ahead on the road, when really all it is, is an illusion. It is caused by when cool layers of air lie above warm layer of air. what your eyes see is a virtual image of the sky below the road.

There is also superior mirages which makes the object seem more up and farther away when really it is just denser layer's of air lie below less dense layer's. In this case light refracts towards the denser air, causing the image to look displaced upward.

We also answer some questions out of the text book Physics 11.

On Tuesday we just continued working on our assignments from the previous day and got our review for our test on Tuesday 29 2011.

Then on Wednesday Mr.Banow came back and we reviewed what we did in Monday and Tuesday's classes.

The next person to write the blog is the last person to have gotten a calculator for christmas...*cought* Mr. Banow! jk The last person with the most letters in there full name.

Total Internal Reflection

In Fridays we discussed the critical angle, which is the measure of the angle of incidence when the angle of reflection is 90 degrees. If the angle of incidence is greater than the critical angle, total internal reflection occurs.

Total internal reflection only occurs when the following conditions are met:

• a light ray is in the more dense medium and approaching the less dense medium.
• the angle of incidence for the light ray is greater than the so-called critical angle.

when the angle of incidence in water reaches a certain critical value , the refracted ray lies along the boundary, having an angle of reflection of 90-degrees. this angle of incidence is know as the critical angle and is the largest angle of incidence for which refraction can still occur. for any angle of incidence greater than the critical angle, light will undergo total internal refraction.

The critical angle can be calculated from Snell's law by setting the refraction angle equal to 90-degrees.

The next blog post will be written by whoever works at Ricks place.

Refraction and Snell's law

In the last two days of class we learnt about the Absolute Index of Refraction, Snell's law and Finding Lateral Displacement.

- The speed of light in a material varies with the density of the material. The number tells us the density of a material is called the index of refraction.

- Changes in the light that are caused by the light entering different materials is called refraction.

n=c/v

n - absolute index of refraction

c - 3.0 x 10(to the power of 8), speed of light in vacuum

v - speed of light in a given material

The higher the index of refraction for a material/medium the more dense it is, therefore the slower the light travels.

Ex: calculate the speed of light in lucite.

n=c/v

v=?

c=3.0 x 10(to the power of eight.. no idea how to do that)

n=1.52

v=c/n v=3.0 x 10^8/ 1.52

v=1.97 x 10^8 m/s

Snell's law

n1 (sin 0i) = n2 (sin 0R)

n = index of refraction for each substance

0i = angle of incidence

0R = angle of refraction

sorry i couldn't keep going but we had valleyball practice and left early for Rosetown because the roads were bad

The Mathematics behind Curved Mirrors

Today in Physics 20 we started the class by viewing the a blog post from the previous day which we usually do. We also reviewed any questions and went over the difference between a converging mirror and a diverging mirror where Mr.Banow also brought out some examples to show the class.

For most of the period we individually worked on our "Curved Mirror Question Package" which had a variety of questions about curved mirrors (diverging, converging). some questions asked us to draw the rays of light and image on a converging or diverging mirror. some questioned asked what the image would look like when the object was placed in a different place in front of the converging/diverging mirror.

ex:

If the object is placed in front of a converging mirror at C, then the image will be inverted, real, the same size and at C.

Near the end of the package there where mathematical questions using the formulas we learned in class to find measurements such as:

hi: hight of the image

ho: hight of the object

di: the distance between the mirror and the image

do:the distance between the mirror and the object

M: Magnification (x)

In the last 5 minutes of class Mr.Banow showed us a pencil in a glass of water allowing us to describe what the pencil had looked like (broken, and larger) and also showing us how it looked upright (just larger)

The next person to write blog post will be the person who has their birthday next

real world aplications of curved mirrors

we started class on Wednesday by thinking of different applications or curved mirrors

some examples are your right handed side mirror on your car, your head lights, flash lights and a disco ball

we also looked at two different types of telescopes

1 -light from distant stars enter the telescope tube in parallel rays

-these rays are reflected from a concave mirror to a diagonal plane mirror
-the diagonal plane mirror reflects the light to the eye piece which then focuses the light

-the larger the diameter of the mirror the brighter the light at the focus new telescopes can have diameters of up to 6m

2.cassegrain reflection telescope

-light rays reflect off a con crave mirror to a perpendicular plane mirror

-rays from the plane mirror proceed to and eye piece at the front which focuses the light.

the next person to write the blog post for today will be decided by the person who is wearing the most blue

Curved Mirror Formulas

During this class we began working on a Practice sheet of curved mirror problems.
We used the following formulas:

M= hi/ ho = -di/do

1/di + 1/ do = 1/f

    Th Curved Mirror formula sheet is also useful.
The next person to blog will be the person wearing the most red.

Locating Images on Curved Mirrors and the Curved Mirror Equation

Last day in class we looked at locating images on converging and diverging mirrors.

Converging Mirror

• the image is in front of the mirror and is between C and F
• the imge is real
• the image is inverted
• the image is smaller

Diverging Mirror

• the image is behind the mirror
• the image is virtual
• the image is upright
• the image is smaller

Note: Some rays near the edge of a spherical converging mirror may not be reflected right through the principle focus. This is called spherical aberration. This can be avoided by using parabolic mirrors. When drawing ray diagrmas we should "trust" the rays closer to the middle of the mirrors.

Today in class we looked at Curved Mirror Equations

M= hi/ho=-di/do 1/di+1/do=1/f

Sign Rules:

1. All distances are measured from the vertex of the mirror
2. Real images have a positive distance
3. Virtual images have a negative distance
4. Postitive Height and Magnification= Upright
5. Negative Height and Magnification= Inverted
6. Focal length of a diverging mirror is negative

Examples

1. A candle is located 30.0 cm from a converging mirror with a radius of curvature that is 10.0 cm

a) At what distance from the mirror will the image be formed?

• do=30.0cm
• f= 10.0/2= 5.0cm ( positive because the mirror is converging)
• di=?

• 1/di+1/do= 1/f
• 1/di+1/30.0 cm= 1/5.0cm
• 1/di=1/5.0 cm- 1/30.0 cm
• 1/di= 1/6
• di= 6.0 cm

b) If the candle is 4.0cm tall, how tall will it's image be?

• ho= 4.0 cm
• hi=?

• hi/ho=-di/do
• hi/4.0cm=-6.0cm/30.0cm
• hi=4.0cm(-6.0cm)/30.0 cm
• hi= -0.80 cm (inverted)

c)What are the characteristics of the image?

• in front (di positive) between C and F
• real (di positive)
• inverted (hi negative)
• smaller (hi

2. A pencil is located 30.cm from a diverging mirror with a focal length of 20.cm

a) where will the image be located?

• do=30. cm
• f=-20. cm (negative because the mirror is diverging)

• 1/di+1/do=1/f
• 1/di+ 1/30 cm= 1/-20 cm
• 1/di=1/-20 cm - 1/30 cm
• 1/di=-1/12
• di=-12 cm

b) If the pencil is 7.0 cm tall, how tall will it's image be?

• ho=7.0 cm
• hi= ?

• hi/ho= -di/do
• hi/7.0cm= -(-12cm)/3.0 cm
• hi= (12 cm)(7.0 cm)/30 cm
• hi= 2.8 cm

c) What is the magnification of the mirror?

• M=?
• M=hi/ho = 2.8cm/7.0 cm
• M= 0.40 x

d) what are the image's characteristics?

• behind mirror (di negative) between V and F
• virtual (di negative)
• upright (hi and M poitive)
• smaller (M<1)

Finding Images in Converging Mirrors

On Tuesday we started the next part of the light unit on curved mirrors. We learned that there are two types of curved mirrors, converging (concave) and diverging (convex) mirrors. There is a principal axis, and on it there is a focal point which we label F and a centre of curvature which we label C. At the point where the principal axis meets the mirror we label V for vertex.

 

We also learned the rules for locating images in curved mirrors. They are as follows:

1. An incident light ray that is parallel to the principal axis will reflect through the focus.

2. An incident light ray that travels through the focus will reflect back parallel to the principal axis.

3. An incident light ray that passes through the centre of curvature will reflect straight back along the same path.

We then looked at the rules for drawing ray diagrams for curved mirrors. They are:

1. Objects are drawn to the left of the mirror.

2. F and C must be measured to scale.

3. Every image has four characteristics:

*Position-relative to the mirror, F, C and V

*Type-real or virtual

*Attitude-upright or inverted

*Magnification-smaller, larger or the same size

Using these rules, we did some examples on how to draw these diagrams for concave mirrors.

http://www.physicsclassroom.com/mmedia/index.cfm#optics

The next person to write the blog will be the person wearing the most black tomorrow. 

Applications of Reflection

At the beginning of class we had a review of the previous class and got time to work on our test review. We also were informed that we were going to get a practice test to work on today in preperation for our unit exam.

After that we took notes on the Applications of Reflection.

Diffuse reflection: When parallel rays of light strike a rough surface they creat different angles of incidence, so light rays reflect in various directions.

Then we learnt about the curved mirrors and will be focusing on mirrors that are cut from spheres.

1. Converging mirrors (concave)

2. Diverging (convex)

We started to take notes on the rules for locating images but the bell rang and we were told we would have more time to look at these notes tomorrow.

Mr. Banow looked like he thoroughly enjoyed dressing up this year and actually came close to looking like Albert Einstein....

I have no idea who is left to write the blog so I will pick someone tomorrow in class.

Locating and Finding the Number Images Through Mirrors at Any Angle

Last day we went over the laws of reflection.
The laws are:
- The angle of incidence is always equal to the angle of reflection.
- The incident ray, reflected ray and the normal all lie in the same plane.
We also looked at how to locate images from a point object and from a larger object.
Point Object(left) Large Object(right)



Today, we looked at how to find the number of images formed for one object when two mirrors are at any angle.

The equation for this type of problem is:





Examples:
a) 45 degrees- N= 360/45-1= 7 images
b) 180 degrees- N= 360/180-1= 1 image
c) 100 degrees- N= 360/100-1= 2.6 images
d) 0 degrees- N= 360/0-1= undefined

Then we learned how the eye sees the middle image when two mirrors are set at 90 degrees with an object places in the center of the mirrors. We found that the middle image does not actually exist. But, it is a reflection from either the first or second image.



The last thing we looked at was how the human eye can see images by looking through a periscope. We learned that the image from the top mirror is laterally reversed, but the bottom mirror reverses the image from the top mirror, resulting in an image that is normal.



The next person to write the blog will be Hilgy's :)