Light: Refraction - Ms. Maier's Science Weebly

$Page 1: Light: Refraction - Ms. Maier's Science Weebly$
Light: Refraction A. Calculate the index of refraction (n) of a material using the speed of light.

The speed of light changes depending on the medium through which it passes. thick medium = ________________ light speed

The index of refraction (n) is a description of the speed of light in a particular media relative to the speed of light in a vacuum.

n = speed of light in a vacuum = 3.00 x 108 m/s speed of light in media v

Air (n =___________) will have little effect on the speed of light Light will slow down considerable in diamond (n = ______________)

o Formula: n = c = 3.00 x108 m/s V V

Sample problems: 1. The speed of light in a liquid is 2.25 x 108 m/s. What is

a. the refractive index of the liquid?

b. the liquid? ________________

2. Calculate the speed of light in diamond.

3. Rank the materials – water, ruby, air, zircon - based on the a. index of refraction (or optical density), n, from least to greatest;

b. speed of light in them, from least to greatest.

B. Explain why refraction occurs. o Demo: refraction of light in air and a glass block o Jot notes: Refraction

Light rays can be bent as they travel from one media into another; this is known as ____________________________.

This occurs because the speed of light changes as it passes into the new media. Light will mostly pass through a thicker (optically dense) media but some can undergo

____________________________. Light bends ____________________________the normal when it passes into an optically dense

media. Light bends ____________________________the normal when it passes into a less dense

substance.

There is ____refraction if the i = 0 (along the normal).

Indices of Refraction

Substance Index of

Refraction (n)

Vacuum 1.0000

Air (00C, 101KPa) 1.0003

Water 1.33

Ethyl alcohol 1.36

Quartz (fused) 1.46

Glycerine 1.47

Lucite or Plexiglass 1.51

Glass (crown) 1.52

Sodium chloride 1.53

Glass (crystal) 1.54

Ruby 1.54

Glass (flint) 1.65

Zircon 1.92

Diamond 2.42

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o Sample problems:

Predict the direction light bends compared to the normal. Light passes from a. water into zircon;

light bends towards the normal OR away from the normal b. diamond into air;

light bends towards the normal OR away from the normal c. crown glass into flint glass

light bends towards the normal OR away from the normal d. ruby into quartz into water

light bends towards the normal OR away from the normal

o Practice:

1. What is the index of refraction (n) of a liquid in which the speed of light is 2.50 x 108 m/s? (n= 1.20) 2. What is the speed of light in sodium chloride? (v= 1.96 x 108 m/s)

3. Zircon is often used as an imitation diamond in costume jewellery. Calculate how much the speed of light changes when it passes from air into zircon. (HINT: find the difference in speed between air and zircon) (v= 1.44 x 108 m/s)

4. How long (what time) will it take light to travel through a piece of quartz 1.00 m thick? Recall: v = d/t (t=4.88 x 10-9 s)

5. The speed of light in three different media is as follows: a. 2.25 x 108 m/s b. 1.24 x 108 m/s c. 1.95 x 108 m/s

Determine the index of refraction of each medium, and, using the table of indices of refraction, identify the medium in each case.

(a. n= 1.33, water b. n= 2.42, diamond c. n= 1.54, glass/crystal or ruby)

6. The speed of light in plastic is 2.0 x 108 m/s. what is the refractive index of plastic? (n=1.5)

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7. The index of refraction of crown glass for violet light is 1.53, and for red light it is 1.51. Assuming the velocity of light in a vacuum is 3.00 x 108 m/s, what are the speeds of violet light and red light in crown glass? (vv=1.96 x 108 m/s; vr=1.99 x108 m/s)

8. The index of refraction for blue light in glass is slightly higher than that for red light in glass. What does this indicate about

a. The relative speeds of red light and blue light in glass, and blue light (higher n) thin OR thick fast OR slow red light (lower n) thin OR thick fast OR slow

b. The angles of refraction for each colour, for the same angle of incidence?

blue light (higher n) bends less OR bends more smaller angle OR larger angle

red light (lower n) bends less OR bends more smaller angle OR larger angle

9. Relate each of the following terms to one of the numbers:

angle of incidence - # ___ normal - # ___

refracted ray - # ___ angle of reflection - # ___

incident ray - # ___ angle of refraction - # ___

reflected ray - # ___

10. For each of the following, draw in the general direction of the refracted ray(s) in each case.

o Lab: Refraction of Light

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C. Calculate the index of refraction (n) of a material using incident and refracted angles.

Formula: n1sin1 = n2sin2

o Jot Notes: Snell’s Law

Snell’s Law can be used to calculate the refraction (bending) of light passing from one material into another:

n1sin1 = n2sin2 n1 = index of refraction of 1st material

1 = incident angle (in 1st material) n2 = index of refraction of 2nd material

2 = refracted angle (2nd material)

o Sample Problems: 1. Suppose air is the first material and only three sig figs are needed. Simplify the formula.

2. Light passes from air into water. If the angle of incidence is 30.0, what is the angle of refraction?

3. If the index of refraction for diamond is 2.42, what will be the angle of refraction in diamond for

an angle of incidence, in water, of 60.0?

4. What is the index of refraction of an unknown material if the angle of incidence in water is 32.00 and the angle of refraction in the material is 27.60?

5. If light in a pet store approached the glass (crown) of an aquarium at an angle of 25.00C, then the light passed through the glass into the water of the aquarium, what would the angle of refraction be in the water? Air Glass Water

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o Practice: 1. Light passes from air into diamond with an angle of incidence of 60.0. What will be the angle of

refraction? (θ2=21.00)

2. A transparent substance has a refractive index of 1.30. What is the angle of incidence in air when the

angle of refraction in the substance is 45.0? (θ1=66.80)

3. What is the index of refraction of a material if the angle of incidence in air is 50.0 and the angle of

refraction in the material is 40.0? (n2= 1.19)

4. A diver shines her flashlight upward from beneath the water at an angle of 30.0 to the vertical. At what angle does the beam of light emerge from the water into the air? (θ2=41.70)

5. An underwater swimmer looks up towards the surface of the water on a line of sight that makes an angle

of 25.0 with a normal to the surface of the water. What is the angle of incidence in air for the light rays that enter the swimmer’s eye? (θ1=34.20)

6. A beam of light from air is directed on the flat surface of a block of fused quartz at an angle of 46.90. The light then moves through ruby. What is the angle of refraction in ruby? Air Quartz Ruby (θ=28.30)

7. A coin lies on the bottom of a swimming pool as illustrated in the diagram. A flashlight beam is directed over the edge of the pool to illuminate the coin. At what angle relative to the pool wall must the flashlight be aimed? (θ1=58.30)

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D. Recognize and analyse situations where a refracted angle of 90 (total internal reflection) can be produced.

o Formula: n1sinc = n2sin2 c = 90 When light passes from a thick (optically dense) material into a thin material, the ray bends

________________ the normal.

As the angle of incidence (i) increases, the angle of refraction (R) increases. When the angle of refraction equals 90°, this is called the ___________ angle. At the critical angle, most of the light becomes ________________ as it cannot leave the

medium by refraction.

If the i is greater than c the ray will not pass into the second material by refraction; it will reflect inside the first material; this is called _____________ ___________________reflection.

For total internal reflection to occur,

the light must travel from a __________ material to a _________ material (n2 < n1), and

the light must strike the second material at an angle __________ than the critical angle.

The critical angle can be calculated using the equation:

n1sinc = n2sin2 where 2 = 90 = 1

Since sin 900 = 1 and since n2 is most often air (n=1.0003), the equation can be reduced down

to

sinc = 1/n1

o Sample Problems: 1. In which situation will total internal reflection occur – when light passes from water into ruby

or ruby into water?

2. What is the critical angle in crown glass when light passes from crown glass into air?

3. What is the critical angle when light moves from flint glass into fused quartz?

4. The critical angle for a medium is 42.860. What is the index of refraction of the medium? What

substance is it?

5. Light passes from a diamond into air. If the angle of incidence is 35, what is the angle of refraction? What does this answer mean?

Only use this formula if the

second substance is air!

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o Practice: Remember: if a second substance isn’t listed, assume it is air!

1. If the index of refraction for water is 1.33, what is the critical angle for water? (θc=48.80)

2. The critical angle for a medium is 40.5. What is the index of refraction of the medium? (n=1.54)

3. What is the critical angle if the index of refraction for a medium is 1.68? (θc=36.50)

4. What is the index of refraction of a medium if the critical angle is 40.0? (n=1.56)

5. What is the critical angle for light moving from zircon into ethyl alcohol? (θc=45.10)

6. From the inside of an aquarium, a ray of light is directed from the water to the glass so that the angle of

incidence is 30.0. a. Determine the angle of refraction when the ray emerges from the glass into the air. (water

glass air) (θair=41.70)

b. If the angle of incidence in the water is 52.0, at what angle will the rays emerge from the glass

into the air? (θair=error; total internal reflection)

o Lab Manual: Total Internal Reflection o Hand in: Light

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Lenses A. Distinguish between types of lenses.

A lens is made of ______________________ material Lenses have a PA, F, C (labeled 2F) and f just like mirrors.

B. Diagram converging and diverging lenses and their images.

Convex/Converging Lenses A convex/converging lens is _____________ at the center than

at the edges. Light passing through __________________ to the focal point.

The primary focus (F) is on the ______________ of the lens, and the secondary focus (F|) is on the _____________.

You could turn the lens around, and it will _________________________________. Ex) magnifying glass

Concave/Diverging Lenses

A concave/diverging lens is _____________ at the center.

Light passing through diverges ___________ from the focal point. The focuses are ___________ in concave lenses. (F) is on the left

of the lens, and the secondary focus (F|) is on the right.

When light passes through a lens, _____________ occurs at the two lens surfaces.

Using Snell’s law and geometry, you can predict the paths of rays passing through lenses.

Convex/Converging Lenses

A convex lens causes all rays to ______________________.

Rules for Drawing Rays for Convex/Converging Lenses 1. Any incident ray traveling parallel to the principal axis of a converging lens will refract

________________ the lens and travel through the ______________ point on the ______________ side of the lens.

2. Any incident ray traveling through the __________ point on the way to the lens will refract through the lens and travel ______________________ to the principal axis.

3. An incident ray that passes through the center of the lens will in effect ______________ in the same direction that it had when it entered the lens.

Sample Problems:

http://www.bbc.co.uk/schools/gcsebitesize/science/images/edex_phy_lens_lrg.jpg

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For a Convex/Converging Lens the ________________, ___________________, and __________________ of the image depend on where the object is located.

As long as the object is ________________ the focal point the image is real and inverted. When the object is _______________ the focal point the image becomes virtual and upright.

Ex) Object Between F and the lens (O).

Rays 1 and 2 diverge as they leave the lens thus, ____ real image is possible.

Drawing _____________ lines for the two rays back to their apparent intersection locates the virtual image.

The image is on the __________ side of the lens as the object, and it is ________________ and _______________ compared to the object.

Practice Problems: Converging Lenses For the following lenses and corresponding object positions, construct ray diagrams. Next, the Orientation (O: upright or inverted), Size of image (S: Magnified, reduced OR SAME size), and the type of image (T: Real or virtual)

Description of Image

NO IMAGE Upright OR Inverted Larger OR Smaller OR Same Size Real OR Virtual



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Concave/Diverging Lenses

A concave lens causes all rays to _______________________.

Rules for Drawing Rays for Concave/Diverging Lenses 1. Any incident ray traveling parallel to the principal axis of a diverging lens will refract through the

lens and travel ________________________ the focal point (i.e., in a direction such that its extension will pass through the focal point).

2. Any incident ray traveling towards the focal point on the way to the lens will refract through the lens and travel ___________________ to the principal axis. The parallel line will be reflected back towards the object side of the lens.

3. An incident ray that passes through the center of the lens will in effect ______________ in the same direction that it had when it entered the lens.

Sample Problems:

The image is located at the point from where the two rays apparently diverge. Because the rays diverge, they produce a _______________ image.

The image also is ______________ and _____________ compared to the object.

This is true no matter how far from the lens the object is located.

The focal length of a concave lens is ________________________.

The image is always ___________ and is located between the ___________ and the lens. Practice Problems: Ray Diagram Practice

1. For the following lenses and corresponding object positions, construct ray diagrams. Next, circle the Orientation (O: upright or inverted), Size of image (S: Magnified or reduced), and the type of image (T: Real or virtual)



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Case 3: If the object is located between F and 2F.

2. Write the names of each of the numbered parts:

C. Use the lens to determine characteristics of objects and images. o Formulae: 1 + 1 = 1 m = hi = - di

do di f ho do

Sign Convention

• f is _____ if the lens is a double convex lens (converging lens) • f is _____ if the lens is a double concave lens (diverging lens) • di is _____ if the image is a real image and located on the opposite side of the lens. • di is _____ if the image is a virtual image and located on the object's side of the lens. • hi is _____ if the image is an upright image (and therefore, also virtual) • hi is _____ if the image an inverted image (and therefore, also real) • m is _____ for an erect image • m is _____ for an inverted image.

NOTE:

A converging lens has a ___________ principal focus and a ________________ focal length.

A diverging lens has a _____________ principal focus and a ________________ focal length.



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Sample Problem: An object is placed 32.0 cm from a convex lens that has a focal length of 8.00 cm.

a. Where is the image?

b. If the object is 3.0 cm high, how tall is the image?

c. What is the orientation of the image? Upright OR Inverted Practice Problems:

1. Locate the position of the image of a candle placed 20.00 cm in front of a converging lens of focal length 25.00 cm. (-100.0cm; virtual image)

2. Locate the image of an object that is 15 cm in front of a diverging lens of focal length 25 cm. (-9.4 cm; virtual image)

3. A lamp 10.0 cm high is placed 60.0 cm in front of a diverging lens of focal length 20.0 cm. Locate the image and determine its height. (di=-15.0cm; hi=2.50cm) (virtual and upright)

4. If the image in a convex mirror is 15.0 cm tall in the mirror, appearing exactly one fourth the actual size, what is the height of the object? (60.0 cm)

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D. The use of lenses in vision correction.

The eyes of many people do not focus sharp images on the ________________.

Instead, images are focused either in front of the retina or behind it.

External lenses, in the form of _________________________ or _________________ lenses, are needed to adjust the focal length and move images to the retina.

Nearsightedness (myopia) is where the focal length of

the eye is too _______________ to focus on the retina.

Images are formed _________________ of the retina.

Correcting for Nearsightedness

_________________ lenses correct this by

____________________ light, thereby increasing the

images’ distances from the lens, and forming images

on the retina.

Farsightedness (hyperopia) is the condition in which the

focal length of the eye is too _______________. Images

are, therefore, formed _____________ the retina.

A similar result is caused by the increasing

__________________ of the lenses in the eyes of people

who are more than about 45 years old. Their muscles

cannot ________________ the focal length enough to

focus images of close object on the retina.

Correcting for Farsightedness

For either defect, convex lenses produce virtual images _______________ from the eye than the associated objects. The image from the lens becomes the object for the eye, thereby correcting the defect. Applications of Lenses

Refracting Telescopes

Binoculars

Cameras

Microscopes

Documents

Light: Refraction - Ms. Maier's Science Weebly