Unit  7  Light  and  Optics  Day  1  Introduction  to  Light  

The  Identities  Crisis    Light   is  made   up   of   _________________   radiations;   on   one   hand,   it  exhibits   ______________   properties   like   waves,   it   has   no   ________   and   it   can  travels   with   ________________.   On   the   other   hand,   light   acts   like   matter   carrying  _____________  and  moving  in  discrete  packets  like  particles  called  __________.  This  is  called  the  Wave-­‐Particle  Duality.    The  Creation  of  Light    

 Step  1    Step  2    Step  3  

 Different  Types  of  EMR  aka  Light  aka  Photons  An  electromagnetic  wave  is  simply  a  light  wave.  However,  we  reserve  the  term  light  for  the  part  of  the  spectrum  we  can  see.  This  is  called  the  _____________  of  the  spectrum.  Other  parts  of  the  spectrum  have  different  names.  It  is  important  to  note  that  each  type  of  wave  is  a  light  wave,  but  just  has  a  different  _________,  _________,  and  behaviours/purposes.    The  electromagnetic  spectrum  is  the  range  of  wavelengths  that  light  can  exist  in.  

   Radio  Waves   _____-­‐energy,  _____  wavelength.  We  use  them  to  broadcast  AM  and  FM  radio  signals,  CB  radio  and  

(back  in  the  day)  antenna  TV  signals.    Microwaves   Still  quite  low-­‐energy.  It  is  useful  in  a  day-­‐to-­‐day  basis  because  ___________  absorbs  them  very  

efficiently.  As  such,  adding  ____________  to  food  makes  it  heats  it  up  more  quickly.    

 

 

Infrared   This  type  of  radiation  is  emitted  by  hot  objects  (Heat‼)  and  is  the  basis  for  ____________________.    Visible  Light   This  tiny  portion  of  the  EMR  spectrum  that  can  be  detected  by  human  eyes.  Visible  light  have  

wavelengths  from  about  400nm  (_______)  to  700nm  (______).    White  light  is  actually  a  mixture  of  many  different  colours  ______________________________________________.  (1𝑛𝑚 = 1×10!!𝑚)  

 Ultraviolet   This  type  of  radiation  is  emitted  in  abundance  by  the  sun,  but  much  of  it  is  blocked  by  the  ___________  

(the  ozone  layer).  It  can  cause  damage  to  cells  at  the  DNA  level,  which  can  in  turn  cause  skin  cancer.      X-­‐Rays   These  are  high-­‐energy  EMR  waves  that  can  penetrate  flesh  but  not  _______,  which  is  why  we  can  use  

them  to  produce  x-­‐ray  images.  The  penetrative  nature  of  x-­‐rays  compared  to  UV  means  that  cell  damage  may  occur  in  any  ____________  in  the  body.  

 Gamma  Rays   The  most  energetic  form  of  EMR.  Emitted  in  ____________________  where  a  nucleus  breaks  apart;  

some  electrons  undergo  huge  energy  level  drops  in  the  process,  emitting  very  energetic  __________.  With  even  better  penetration  than  x-­‐rays,  gamma  rays  can  be  very  useful  in  medicine,  but  similarly  will  increase  the  risk  of  ___________________with  exposure.  

 Light  Rays  

When  light  travels  through  space,  we  generally  represent  it  with  an  arrow  showing  the  direction  it  moves  in.  We  generally  assume  that  light  travels  in  _____________________  

       When  a  light  ray  hits  a  surface,  it  may  be  _________________  (bounce  off),  ________________  (the  surface  gains  energy  as  it  absorbs  the  light  –  think  black  surfaces  in  the  sun)  or  ______________________  (go  through)      Transparent:  transmit  _______  of  the  light,  __________________  gets  absorbed  or  reflected    Ex,    ________________________________  

Translucent:  transmit  light  with  _________________/scattering    Ex)  ____________________________  

Opaque:  doesn’t  transmit  light,  light  is  ________________  or  ______________      Ex)_____________________________  

 Speed  of  light    • In  vacuum,  the  speed  of  light  is  𝑐 = ______________  • In  other  medium,  light  will  slow  down  • In  general,  higher  _____________  →  ____________  speed  of  light    

Equations:  

 Color          • the  color  of  an  opaque  object  is  due  to  the  color  that  it  ___________.    • A  black  object  ________  all  color  and  a  white  object  _______  all  color.    • The  color  of  a  transparent  object  is  due  to  the  combining  of  ____________  light  colors.  https://phet.colorado.edu/sims/html/color-­‐vision/latest/color-­‐vision_en.html  

 

 

 

Worksheet  1:  Introduction  to  light    1. The  wavelength  of  blue  light  is  about  4.5𝑥10!!  m.  Convert  this  to  nm.    2. As  a  spacecraft  passes  directly  over  Cape  Canaveral,  radar  pulses  are  transmitted  toward  the  craft  and  are  then  

reflected  back  toward  the  ground.  If  the  total  time  interval  was  3.00  ×  10–!  s,  how  far  above  the  ground  was  the  spacecraft  when  it  passed  over  Cape  Kennedy?  

3. It  takes  4.0  years  for  light  from  a  star  to  reach  Earth.  How  far  away  is  this  star  from  Earth?  4. The  planet  Venus  is  sometimes  a  very  bright  object  in  the  night  sky.  Venus  is  4.1  ×  10!"  m  away  from  Earth  when  it  

is  closest  to  Earth.  How  long  would  we  have  to  wait  for  a  radar  signal  from  Earth  to  return  from  Venus  and  be  detected?  

5. The  distance  from  Earth  to  the  moon  is  about  3.8×10!  m.  A  beam  of  light  is  sent  to  the  moon  and,  after  it  reflects,  returns  to  Earth.  How  long  did  it  take  to  make  the  round  trip?  

6. A  baseball  fan  in  a  ballpark  is  101  m  away  from  the  batter’s  box  when  the  batter  hits  the  ball.  How  long  after  the  batter  hits  the  ball  does  the  fan  see  it  occur?  

7. A  radio  station  on  the  AM  band  has  an  assigned  frequency  of  825  kHz  (kilohertz).  What  is  the  wavelength  of  the  station?  

8. What  is  the  name  given  to  the  electromagnetic  radiation  that  has  a  wavelength  slightly  longer  than  visible  light?  9. What  is  the  name  given  to  the  electromagnetic  radiation  that  has  a  wavelength  slightly  shorter  than  visible  light?  

 

Physics 11 - Light and Optics Day 2 The Laws of Reflection and Refraction

Reflection

Law of Reflection: 𝜽𝒓 = 𝜽𝒊

_______________ Reflection

o _______________ light rays are reflected _______________

_______________ Reflection

o _______________ light rays are _______________ by irregularities in the surface.

Plane Mirror

o Image is _______________

o Image is _______________ size

o Image is _____________ as far ___________ the mirror as you are in ___________ of it

Since light rays appear to come from _______________

mirror, the image is called a _______________ image.

If light rays _______________ to come from a _______________

location, the image is called a _______________ image.

Real images can be _______________ on a screen, virtual

images _______________.

______________ mirrors only produce _____________ images.

How long must a plane mirror be to see your whole reflection?

Refraction

Speed of light in a vacuum: 𝑐 = 3.00 × 108𝑚

𝑠

Light travels ____________ through materials due to light

___________, absorbed by, emitted by, and scattered by ___________.

Index of Refraction

_______________to indicate relative _______________ of

light in a _______________

𝑛 =𝑐

𝑣

When light hits the surface of a material part of

it is _______________

The other part goes into the _______________

The transmitted part is __________ (_______________)

Snell’s Law (The Law of Refraction)

𝒏𝟏 𝒔𝒊𝒏𝜽𝟏 = 𝒏𝟐 𝒔𝒊𝒏 𝜽𝟐

Where 𝑛1 = index of refraction of incident medium, 𝑛2 = index of refraction of second

medium, 𝜃1 = angle of incidence (measured to normal), 𝜃2 = angle of refraction (measured to normal)

You shine a laser into a piece of clear material. The angle of incidence is 35°. You measure the angle of refraction as 26°. What

is the material?

What is the speed of light in the material?

Physics 11-Day 2 The Laws of Reflection and Refraction Name: ____________________________

Worksheet #2

1. Using the law of reflection, explain how powder takes the shine off of a person’s nose. What is the name of the opticaleffect?

2. Diffusion by reflection from a rough surface is described in this chapter. Light can also be diffused by refraction. Describehow this occurs in a specific situation, such as light interacting with crushed ice.

3. Will light change direction toward or away from the perpendicular when it goes from air to water? Water to glass? Glass toair?

4. Explain why an object in water always appears to be at a depth shallower than it actually is? Whydo people sometimes sustain neck and spinal injuries when diving into unfamiliar ponds orwaters?

5. Suppose a man stands in front of a mirror. His eyes are 1.65 m above the floor, and the top of hishead is 0.13 m higher. Find the height above the floor of the top and bottom of the smallest mirrorin which he can see both the top of his head and his feet. How is this distance related to the man’sheight? (OpenStax 25.1) bottom 0.825 m, top 1.715 m; not related

6. Show that when light reflects from two mirrors that meet each other at a right angle, the outgoingray is parallel to the incoming ray, as illustrated in figure 1. (OpenStax 25.2) See below

7. Light shows staged with lasers use moving mirrors to swing beams and create colorful effects. Show that a light rayreflected from a mirror changes direction by 2θ when the mirror is rotated by an angle θ. (OpenStax 25.3) See below

8. What is the speed of light in water? In glycerine? (OpenStax 25.5) 𝟐. 𝟐𝟓 × 𝟏𝟎𝟖 m/s, 𝟐. 𝟎𝟒 × 𝟏𝟎𝟖 m/s

9. Calculate the index of refraction for a medium in which the speed of light is 2.012 × 108 m/s, and identify the most likelysubstance based on Table 25.1. (OpenStax 25.7) 1.490, polystyrene

10. In what substance in Table 25.1 is the speed of light 2.290 × 108

m/s? (OpenStax 25.8) ice at 0° C

11. Components of some computers communicate with each otherthrough optical fibers having an index of refraction n = 1.55. Whattime in nanoseconds is required for a signal to travel 0.200 mthrough such a fiber? (OpenStax 25.11) 1.03 ns

12. (a) Using information in Figure 2, find the height of theinstructor’s head above the water, noting that you will first have tocalculate the angle of incidence. (b) Find the apparent depth of thediver’s head below water as seen by the instructor. (OpenStax25.12) 2.93 m, 1.37 m

13. Suppose you have an unknown clear substance immersed inwater, and you wish to identify it by finding its index of refraction.You arrange to have a beam of light enter it at an angle of 45.0°,and you observe the angle of refraction to be 40.3°. What is theindex of refraction of the substance and its likely identity?(OpenStax 25.13) 1.46, fused quartz

Figure 1

Figure 2

Figure 4 Answer

to #6 Figure 3 Answer to #7

Physics 11-Light and Optics Day 3 Total Internal Reflection Name: _____________________________

Total Internal Reflection

When light hits an _______________ between two types of _______________ with different indices

of _______________

o Some is _______________

o Some is _______________

Critical angle

o Angle of _______________ where _______________ angle is _______________

o Angles of incidence _______________ than this cause the _______________ angle to be

_______________ the material. This can’t happen, so _______________ refraction occurs.

o 𝜃𝑐 = sin−1𝑛2

𝑛1

Where 𝑛1 > 𝑛2

What is the critical angle from cubic zirconia (n=2.16) to air? Will an angle of 25° produce total

internal reflection?

Uses of total internal reflection

_______________ _______________ for

o Endoscopes

o Telecommunications

o Decorations

_______________ /telescopes

o Makes them shorter

Reflectors

Gemstones

o Cut so that light only _______________ at certain _______________

Dispersion

Each __________________ of light has a different _______________ of refraction

o Red — _______________

o Violet — _______________

o When light is refracted, the violet bends more than red, which

_______________ the colors

Rainbows

o __________________ by _______________ with internal _______________

o Rainbows are always the _______________ direction from the sun

Physics 11- Light and Optics Day 3 Total Internal Reflection Name: _____________________________

Worksheet 3

1. A high-quality diamond may be quite clear and colorless, transmitting all visible wavelengths with little absorption.Explain how it can sparkle with flashes of brilliant color when illuminated by white light.

2. The most common type of mirage is an illusion that light from faraway objects is reflected by a pool of water that is notreally there. Mirages are generally observed in deserts, when there is a hot layer of air near the ground. Given that therefractive index of air is lower for air at higher temperatures, explain how mirages can be formed.

3. Verify that the critical angle for light going from water to air is 48.6°. (OpenStax 25.20) 48.6°

4. (a) Verify that the critical angle for light going from diamond to air is 24.4°. (b) What is the critical angle for light goingfrom zircon to air? (OpenStax 25.21) 𝟐𝟒. 𝟒°, 𝟑𝟏. 𝟑°

5. An optical fiber uses flint glass clad with crown glass. What is the critical angle? (OpenStax 25.22) 𝟔𝟔. 𝟑°

6. At what minimum angle will you get total internal reflection of light traveling in water and reflected from ice? (OpenStax25.23) 𝟕𝟗. 𝟏𝟏°

7. You can determine the index of refraction of a substance by determining its critical angle. (a) What is the index ofrefraction of a substance that has a critical angle of 68.4° when submerged in water? What is the substance, based onTable 25.1? (b) What would the critical angle be for this substance in air? (OpenStax25.25) Fluorite, 𝟒𝟒. 𝟐°

8. A ray of light, emitted beneath the surface of an unknown liquid with air above it,undergoes total internal reflection as shown in Figure 1. What is the index of refractionfor the liquid and its likely identification? (OpenStax 25.26) 1.50, Benzene

9. (a) What is the ratio of the speed of red light to violet light in diamond, based on Table25.2? (b) What is this ratio in polystyrene? (c) Which is more dispersive? (OpenStax25.28) 1.020, 1.012, diamond

10. A beam of white light goes from air into water at an incident angle of 75.0°. At whatangles are the red (660 nm) and violet (410 nm) parts of the light refracted? (OpenStax

25.29) 𝟒𝟔. 𝟓°, 𝟒𝟔. 𝟎°

11. By how much do the critical angles for red (660 nm) and violet (410 nm) light differ in a diamond surrounded by air?(OpenStax 25.30) 𝟎. 𝟓𝟏°

Figure 1

Physics 11 - Light and Optics Day 4 Image Formation by Mirrors

Spherical Mirrors

Concave: bends ______________

Convex: bends ______________

______________are always ___________________ to the

surface and pass through the ______________ of

curvature, C.

o Law of Reflection says that the ______________ to the ______________ is the

same for the ______________ and ______________ rays

Principal axis: imaginary line through _________ and the ____________ of the mirror.

Focal point (F): ______________ rays strike the mirror and ______________ at the focal

point.

Focal length (f): distance between ______________ and ______________

Concave mirrors: 𝑓 =1

2𝑅

Convex mirrors: 𝑓 = −1

2𝑅

Spherical aberration

Rays ________ from the principle axis actually cross between ______ and the __________.

Fix this by using a ______________ mirror.

Ray Diagrams

Concave Mirror

Ray 1 – ______________ to principal axis, strikes mirror and reflects through ___________

Ray 2 – Through __________, strikes mirror and reflects ______________ to principal axis

Ray 3 – Through __________, strikes mirror and reflects back through ______________

Object beyond C

Image is ______________, ______________ and ______________, between ______________ and ______________

Object between C and F

Image ______________, ______________, and ______________, beyond ______________

C F Object

C F Object

Physics 11-06 Image Formation by Mirrors Name: _____________________________

Object between F and mirror

Image ______________, ______________, ______________, ______________ mirror

Convex Mirrors

Image ______________, ______________, ______________, ______________ mirror between F and ______________

Mirror Equation

1

𝑓=

1

𝑑𝑜+1

𝑑𝑖

Where f = focal length (negative if ______________), d0 = object distance, di = image distance (negative if ______________)

Magnification Equation

𝑚 =ℎ𝑖ℎ𝑜

= −𝑑𝑖𝑑𝑜

Where m = magnification, ho = object height, hi = image height (negative if ______________), do = object distance, di = image

distance (negative if ______________)

A 0.5-m high toddler is playing 10 m in front of a concave mirror with radius of curvature of 7 m.

What is the location of his image?

What is the height of his image?

A 0.5-m high toddler is playing 10 m in front of a convex mirror with radius of curvature of 7 m.

What is the location of his image?

What is the height of his image?

C F Object

C F Object

Physics 11-04 Image Formation by Mirrors Name: _____________________________

Homework

1. What are the differences between real and virtual images? How can you tell (by looking) whether an image formed by asingle lens or mirror is real or virtual?

2. Can you see a virtual image? Can you photograph one? Can one be projected onto a screen with additional lenses ormirrors? Explain your responses.

3. Is it necessary to project a real image onto a screen for it to exist?

4. Under what circumstances will an image be located at the focal point of a lens or mirror?

5. What is meant by a negative magnification? What is meant by a magnification that is less than 1 in magnitude?

6. What is the focal length of a makeup mirror that has a power of 1.50 D? (OpenStax 25.53) +0.667 m

7. Some telephoto cameras use a mirror rather than a lens. What radius of curvature mirror is needed to replace a 800 mmfocal length telephoto lens? (OpenStax 25.54) +1.60 m

8. (a) Calculate the focal length of the mirror formed by the shiny back of a spoon that has a 3.00 cm radius of curvature. (b)What is its power in diopters? (OpenStax 25.55) −𝟏. 𝟓𝟎 × 𝟏𝟎−𝟐 m, -66.7 D

9. Electric room heaters use a concave mirror to reflect infrared (IR) radiation from hot coils. Note that IR follows the samelaw of reflection as visible light. Given that the mirror has a radius of curvature of 50.0 cm and produces an image of thecoils 3.00 m away from the mirror, what is the magnification of the heater element. Note that its large magnitude helpsspread out the reflected energy. (OpenStax 25.56) -11.0

10. What is the focal length of a makeup mirror that produces a magnification of 1.50 when a person’s face is 12.0 cm away?Solve with both a ray diagram and the mirror equation. (OpenStax 25.57) 0.360 m

11. A shopper standing 3.00 m from a convex security mirror sees his image with a magnification of 0.250. (a) Where is hisimage? (b) What is the focal length of the mirror? (c) What is its radius of curvature? (OpenStax 25.58) -0.750 m, -1.00 m,2.00 m

12. An object 1.50 cm high is held 3.00 cm from a person’s cornea, and its reflected image is measured to be 0.167 cm high. (a)What is the magnification? (b) Where is the image? (c) Find the radius of curvature of the convex mirror formed by thecornea. (Note that this technique is used by optometrists to measure the curvature of the cornea for contact lens fitting.The instrument used is called a keratometer, or curve measurer.) (OpenStax 25.59) +0.111, -0.334 cm, -0.752 cm

Physics 11 - Light and Optics Day 5 Image Formation by Lenses

Lenses

Lens - Made from ___________________ material,

usually with a ______________ edge.

Converging Lens – ______________ middle,

______________ edge (______________)

Diverging Lens – ______________ middle, ______________ edge (______________)

Power of lens

o 𝑃 =1

𝑓

o Unit: ______________ (D)

Ray Diagrams

Converging Lenses

Ray 1 – ______________ to principal ______________, bends through ______________

Ray 2 – Through ______________, bends ______________ to principal axis

Ray 3 – Goes through ______________ of lens, does ______________ bend

Object beyond 2F (case 1)

Image ______________, ______________, ______________, between ______________ and ______________

Object between F and 2F (case 2)

Image ______________, ______________, ______________, beyond ______________

Object between F and lens (case 3)

Image ______________, ______________, between ______________ and ______________ on side with ______________

2F F Object F 2F

2F F Object F 2F

2F F Object

F 2F

Physics 11-05 Image Formation by Lenses Name: ____________________________

Diverging Lens

Ray 1 now bends ______________ from axis so that it looks like it came ______________ F

Ray 2 starts by aiming at ______________ F

Ray 3 same as ______________

Image ______________, ______________, ______________, between ______________ and ______________

Thin-lens equation

1

𝑓=

1

𝑑𝑜+1

𝑑𝑖

Where f = focal length, do = object distance, and di = image distance

Converging Lens

o f ______________

o do ______________ if real (left side)

o di ______________ if real (right side)

Diverging Lens

o f ______________

o do ______________ if real (left side)

o di ______________ if virtual (left side)

Magnification equation

𝑚 =ℎ𝑖ℎ𝑜

= −𝑑𝑖𝑑𝑜

Lens Reasoning Strategy

1. Examine the situation to determine that ______________ formation by a lens is ______________.

2. Determine whether __________ tracing, the __________ lens equations, or __________ are to be employed. A sketch is very

______________ even if ray tracing is not specifically required by the problem. Write symbols and values on the sketch.

3. Identify exactly what needs to be _________________ in the problem (identify the ________________).

4. Make a list of what is ______________ or can be ______________ from the problem as stated (identify the ______________). It is

helpful to determine whether the situation involves a case ______________, ______________, or ______________ image. While

these are just names for types of images, they have certain characteristics that can be of great use in solving problems.

5. If ray tracing is ______________, use the ray tracing ______________ listed near the beginning of this section.

6. Most __________________ problems require the use of the ______________ lens equations.

7. Check to see if the answer is _________________: Does it make ______________? If you have identified the type of image (case

1, 2, or 3), you should assess whether your answer is ________________ with the type of image, magnification, and so on.

A child is playing with a pair of glasses with diverging lenses. The focal length is 20 cm from the lens and his eye is 5 cm from

the lens. A parent looks at the child’s eye in the lens. If the eye is the object, where is the image located?

If his eye is really 3 cm across, how big does it appear?

2F F Object F 2F

Physics 11-05 Image Formation by Lenses Name: ____________________________

Homework

1. When you focus a camera, you adjust the distance of the lens from the film. If the camera lens acts like a thin lens, why canit not be a fixed distance from the film for both near and distant objects?

2. A thin lens has two focal points, one on either side, at equal distances from its center, and should behave the same for lightentering from either side. Look through your eyeglasses (or those of a friend) backward and forward and comment onwhether they are thin lenses.

3. Will the focal length of a lens change when it is submerged in water? Explain.

4. Your camera’s zoom lens has an adjustable focal length ranging from 80.0 to 200 mm. What is its range of powers?(OpenStax 25.37) 12.5 D, 5.00 D

5. What is the focal length of 1.75 D reading glasses found on the rack in a pharmacy? (OpenStax 25.38) 57.1 cm

6. How far from the lens must the film in a camera be, if the lens has a 35.0 mm focal length and is being used to photographa flower 75.0 cm away? Solve using both a ray diagram and the thin lens equation. (OpenStax 25.40) 36.7 mm

7. A certain slide projector has a 100 mm focal length lens. (a) How far away is the screen, if a slide is placed 103 mm fromthe lens and produces a sharp image? (b) If the slide is 24.0 by 36.0 mm, what are the dimensions of the image? (OpenStax25.41) 3.43 m, 80.0 cm × 120 cm

8. A doctor examines a mole with a 15.0 cm focal length magnifying glass held 13.5 cm from the mole (a) Where is the image?(b) What is its magnification? (c) How big is the image of a 5.00 mm diameter mole? (OpenStax 25.42) -1.35 m, +10.0,50.0 mm

9. A camera lens used for taking close-up photographs has a focal length of 22.0 mm. The farthest it can be placed from thefilm is 33.0 mm. (a) What is the closest object that can be photographed? (b) What is the magnification of this closestobject? (OpenStax 25.45) 6.60 cm, -0.5

10. Suppose your 50.0 mm focal length camera lens is 51.0 mm away from the film in the camera. (a) How far away is anobject that is in focus? (b) What is the height of the object if its image is 2.00 cm high? (OpenStax 25.46) 2.55 m, 1.00 m

11. (a) What is the focal length of a magnifying glass that produces a magnification of 3.00 when held 5.00 cm from an object,such as a rare coin? (b) Calculate the power of the magnifier in diopters. (c) Discuss how this power compares to those forstore-bought reading glasses (typically 1.0 to 4.0 D). Is the magnifier’s power greater, and should it be? (OpenStax 25.47)7.50 cm, 13.3 D, lots stronger

12. (a) Where is the image that will be produced by a lens of power –4.00 D (such as might be used to correct myopia) if anobject is held 25.0 cm away? Solve by using both a ray diagram and the thin lens equation. (b) What is themagnification?(OpenStax 25.48) -12.5 cm, +0.500