Experiment 9: Light Phenomena
Alexandra Rebosa, Jan Sanchez, Murielle Santiago Department of Psychology College of Science, ni!ersity of Santo "omas #spa$a, Manila, Philippines Abstract:
Thi This expe experrimen imentt deal dealss wit with the the scientific concepts behind light, such as refraction and reflection. In this experiment, the index dex of refraction of gla glass was determined, ned, along ong with the lateral displa displaceme cement nt of differ different ent light light rays rays going going through a glass plate. Angles of incidence, reflection, and refraction were also obtained in the experiment. The relationship between light ght inte intens nsiity and and dis distanc tancee was was als also determined in the experiment with the help of Logger Logger Pro. Pro. The relat relation ionshi ship p between between intensity and distance was found to be an inverse square relationship. relationship. 1. Introduction
%ight is !ery important to humanity and the &orld' (t is &hat enables a person to see and ma)e sense of the &orld' (t is also the medium in &hich the sun sends out its energy*+, &hich ma)es life on earth possible' p ossible' -ithout light, a person &ill not be able to see anything or ma)e sense out of his or her &orl &orld' d' %ife %ife &ill &ill not not be poss possib ible le &ith &ithou outt light, or more importantly sunlight, since it gi!es energy to li!ing ob.ects such as plants and animals' "he study of light is )no&n as optics' /ptics is a branch of science that studies the important properties of light' A subtopic in optics includes one of the the most most impo import rtan antt prop proper erti ties es of ligh light, t, )no&n as reflection, refraction, and intensity of ligh lightt 0bri 0bright ghtnes ness1 s1'' "he "he prin princi cipl ples es of
reflection, refraction, and intensity &ill be further discussed in the experiment' "his "his experim experiment ent aims aims to determi determine ne the index of refraction for glass and to !erify the la&s of reflection' 2. Theory
%ight does not al&ays go through a smooth straight path &hen it tra!els around throu hrough gh dif differen erentt medi ediums ums' "hus, hus, it experiences bending &hen it tra!els through a denser medium, such as &hen light tra!els from the air through a glass' "his phenomenon is called the refraction of light' "he formal formal defini definitio tion n of the refrac refractio tion n of light is the bending of the light, &hen light arri!es through a different medium &here in its speed is different *+' Moreo!er, light can also be reflected through the use of mirrors, &here in its speed remains constant, since it did did not not pas pass throu hrough gh a medi edium' um' "his his phenomenon could be most li)ely compared to an echo in sound, though in this case the ligh lightt boun bounce cess from from a smoo smooth th and and glas glasss coated surface2a mirror' %ight can be understood through its model of a ray and &a!e front' "he model of a ray can be seen through a focused sample of light &here in it concentrates through a straight line3 &hile the model of the &a!e front can be seen through the circular li)e pro.ection of light from the sun *4' Mainly, the &a!e front connects the rays of light that tra!els form a source, li)e the sun' "hough most the sample of light that the expe experi rim mente enterrs ha!e ha!e expe experi rim ment ented, ed, is
extrinsically can be seen &ith the form of a ray' "he la&s that go!ern &hen light passes through different mediums, such us mirrors and glasses, are the la&s of refraction and reflection' "he la& of refraction, &hich is also )no&n as the Snell5s la&, states that the angle of incidence 06+1, and the index of refraction 0n+1 &here the angle of incidence ha!e occurred is directly proportional to the angle of refraction 0641, and the index of refraction 0n41 &here the angle of refraction occurred' "his is further stated by this e7uation belo&'
n1 sin θ 1=n2 sin θ2
d
Figure 1: The Location o the Latera! "istance o Light
"hus, the lateral distance of light can be sol!ed through this e7uation belo&'
d =tsinθ1 ( 1 − 8asically, the said index of refraction in the aforementioned statement is based on the ratio of the speed of light in !acuum 0c1 to the speed of light in the medium 0!1' "his is correctly represented by the e7uation belo&'
n=
c v
9urthermore, the Snell5s la& can also be expanded and applied through the application of sol!ing for the lateral distance 0d1 of light' "he lateral distance of light is the 4 parallel lines formed by the emergent ray and the continued line of the incident ray' "he lateral distance .ust describes the de!iation of the ray of light or an image to the supposed distance that the incident ray &ill ha!e if it &ere not for the t&o different mediums' "he lateral distance can be best explained through the diagram gi!en belo&'
n1 cos θ 1 n2 cos θ 2
)
"he la& of reflection is different from the la& of refraction3 because the speed of light does not change throughout its reflection on the medium' "his is so because the medium of mirrors are smooth, glassy, and not transparent in nature' 9or &hich it &ould not ha!e any influence of the change of speed in light' "herefore, the angle of incidence 06i1 and the angle of reflection 06r 1 &ill be .ust the same &ith each other *:' "his is seen through this e7uation belo&' 6i ; 6r
"he !alidity of the e7uality of the angle of incidence to the angle of reflection can be sol!ed through the e7uation gi!en
|( )|
difference = belo&'
θ i − θr θi + θr
x 100
2
%ight also beha!es li)e sound &hen pro.ected through a long range' "hus, for the instance &hen sound is pro.ected in a long range, its intensity changes' So as light, the intensity of the light also changes throughout a certain distance' /b!iously, &hen the obser!er of the light is near from a source, the intensity of the light is high3 though &hen the obser!er is far from the source of light, the intensity of the light tends to gradually disappear or be lo&' Actually, there is a la& that go!erns this phenomenon, and it is called the in!erse s7uare la& of intensity, &here in it states that the intensity of a constant intrinsic luminosity of light source from an obser!e point is calculated through, the s7uare of its distance from the point of the source of light to its obser!er *<' "his is portrayed in the e7uation belo&' 1
( ; r2 #. $ethodo!ogy Acti%ity 1: &eraction
"he first acti!ity of the experiment &as di!ided into three parts= (ndex of Refraction for >lass, Refraction through Parallel Plate, and Refraction through a Spherical Surface' A. Index o &eraction or '!ass
"he first part of this acti!ity deals &ith the refraction of certain materials such as glass' "he index of refraction for glass &as determined by using a rectangular glass plate and a protractor' 9irst, the angle of refraction &as determined for each of the follo&ing angles of (ncidence= +?, +@, 4@, :?, :@' ext, a sine of angle of incidence !ersus a sine of angle refraction &as plotted' "he index of refraction &as then determined based on the data obtained from the graph' "he theoretical !alue for the index of refraction of glass &as obtained' %astly, the percent error of the acti!ity &as computed' (. &eraction through Para!!e! P!ate
9irst, a rectangular glass plate &as placed at the centre of the paper' "he outline of a glass plate &as traced &ith a pencil so it may return to its original position &hen mo!ed' %ight from a laser pointer struc) the glass along ray A8' Points C and D &ere mar)ed along the emergent ray' ext, the glass plate &as remo!ed' "he incident ray, the normal to the plate, the angle of incidence, the refracted ray, the angle of refraction, and the angle of the emergent ray &as traced' ext, the angle of incidence and the angle that the emergent ray ma)es &ith the normal &ere measured' "he percent difference &as computed' ext, ray A8 &as extended until it &as sideB byBside &ith ray CD' "he lateral displacement of ray A8 &as measured, and by using a little trigonometry, its theoretical displacement &as computed' %astly, percent difference &as computed'
). &eraction through a *pherica! *urace
A Con!erging lens &ith a ray box or t&o laser pointers pointed parallel to each other &as illuminated' "he obser!ations in this acti!ity &ere dra&n' "he entire procedure &as also repeated using a di!erging lens'
Acti%ity 2: &e!ection
9or the second acti!ity of the experiment, the angle of incidence and angle of reflection &ere measured in the experiment using a laser beam and plane mirror' 9irst, the laser beam &as point at three different angles of incidence to a plane mirror' "he angle of reflection &as measured for each angle of incidence' %astly, the percent difference bet&een the angle of incidence and the angle of reflection &as computed' Acti%ity #: In%erse Intensity
s+uare La,
"he acti!ities to study the beha!ior of light in the experiment had been di!ided into three acti!ities, these pertained acti!ities are= Acti!ity += Refraction3 Acti!ity 4= Reflection3 and Acti!ity := (n!erse S7uare %a& for (ntensity' Acti!ity += Refraction 9or acti!ity one the experimenters has sub.ected the laser pointers to different angles from the normal line' (t is obser!ed that the angle of incidence and refraction are only directly proportional up to some point, because &hen the laser pointer de!iated a&ay from the normal line, and go closer to the horizontal of the glass plate, it got reflected to a certain extent from the glass plate' "his .ust means that at a certain degree of de!iation from the normal line, light &ill ha!e a hard time to penetrate an opa7ue or transparent medium' "hus, it &ill result to the reflection of light to that medium' "his is greatly exemplified to the graph belo&'
or
9or the third acti!ity of the experiment, the relationship bet&een the distance of the light source and its intensity &as determined' A computer &ith %ogger Pro, a light bulb, and a metrestic) &as used for this acti!ity' 9irst, the intensity of a light source to sensor distances of 4@ cm, @? cm, @ cm, +?? cm, +4@ cm, and +@? cm &as determined using a sensor' "he intensity !ersus distance graph &as plotted' -. &esu!ts and "iscussion
Figure 2: 'raph o the *ine Ang!e o Incidence on the y/axis0 %ersus *ine Ang!e o &eraction on the axis0
Since, the experimenters ha!e already experimented upon the beha!iors of light rays to different degrees of de!iation from the normal line3 the experimenters
!erified next the !alidity of the Snell5s la& through the application of computation through different angles' "he experimenters achie!ed this !erification through preciseness of the computed index of refraction of the glass plate through different degrees of the angle of incidence' "he index of refraction of the glass place &as sol!ed through the e7uation belo&'
n2=
"he angle that the experimenters used for the computation of the lateral distance is the angle of
sin θ1 n1 sin θ 2
(t is obser!ed in the table belo& that the experimenters ha!e incurred a :'< amount of percent error &ith the !erification that they conducted' "hus, this indeed .ust pro!es that the !alues computed for &as nearly accurate' And the percent error incurred in the experimental results &as due to the parallax errors in reading the protractor, and the minor unnoticed mo!ement of the glass plate during throughout the actual experiment' Tab!e1. Index o &eraction o '!ass Angle of (ncidence Angle of in Degrees Refraction in Degrees +? '@ 4? +: :? +E'@
#xperimental (ndex of Refraction "heoretical (ndex of Refraction Percent #rror
"hough, e!en if the angle of incidence and the angle of emergence are correctly e7ual &ith each other, the computed lateral displacement still incurred an error of +:':: percent' "his percent error is mainly caused by the possible parallax error in reading the measurement or, incorrectly tracing the incident ray' Tab!e2. &eraction through Para!!e! P!ate Angle of (ncidence
+'<
+'@ :'
"he figure belo& sho&s the beha!ior of light through a spherical surface' "he spherical surfaces that the experimenters used are the con!ex and conca!e glass' "hus, in the con!ex glass all of the lights from the laser pointer &ere refracted to the middle of the focal point3 though, in a
conca!e glass all of the light rays di!erge from one another' "his is exemplified through the image belo&'
from the light source, the lo&er the intensity or brightness that it &ill ha!e' "his is exemplified and pro!en by the graph belo&'
Figure #: &eraction through *pherica! *urace Figure -: Intensity
In%erse
*+uare
La,
or
Acti!ity 4= Reflection "he table belo& explains the comparison of the angle of incidence and the angle of reflection' (t is theoretically assumed that the angle of reflection should be e7ual &ith each other' "hough, through the data belo& there are still percent differences in the comparison of both' "his is so because the mirrors might ha!e been mo!ed in an unnoticed manner by the experimenters, or the light source &as not that focused enough 0the rays is still scattered in some &ay1 to actually dra& an accurate line of the angle of incidence and angle of reflection' Tab!e#. &e!ection Angle of Angle of (ncidence Reflection in Degrees in Degrees + @ @ @ : @@
Percent Difference G' +:':: +:'E
Acti!ity := (n!erse S7uare %a& for (ntensity "his acti!ity .ust pro!es that the farther a&ay the light sensor or the obser!er
. )onc!usion
"he experimenters conducted different acti!ities &herein they experimented upon the beha!iors of light in different situations' 9irst, it has been experimented on ho& light &ill react through different mediums, and spherical surfaces' Second, the intensity of the light &as obser!ed through the !arying distances' "he !arying experiment has pro!en that la&s of refraction, reflection, and in!erse s7uare la& can be experimentally !erified' "hese la&s are experimentally !erified through the determination of the index of refraction of glass, the measurement of the angle of incidence and the angle reflection, and through the logger pro and light sensor' "hough of course the actual experiments ha!e incurred percent errors because of parallax errors, unnoticed mo!ement of the instruments during
dra&ing measurements, and the seemingly unfocused light rays since the room &as not totally dar)' . App!ication 1. *ho, mathematica!!y that a ray o !ight in passing through a para!!e! sided g!ass p!ate emerges para!!e! to its incident path.
%et5s say that 6+;+GH, nair ;+, nglass;+'@4 nair sin6+ ; nglasssin64 Part +
#. )ite some practica! uses o reraction and re!ection o !ight.
(n disco clubs, a mirror ball &ith uniform pieces of mirrors reflects lights onto the people on the dance floor and the surrounding and fiberBoptics also uses the principles of reflection' As for refraction, it is used for lenses in contact lenses, glasses' 6. &eerences
*+ Refraction of light' 0n'd'1 Retrie!ed May +@, 4?+<, from http=IIhyperphysics'phyB astr'gsu'eduIhbaseIgeooptIrefr'html
0+1 0sin+GH1 ; sin64 0+'@41 sin64 ; *0+1 0sin+GH1I +'@4 64 ; ++':H 2. As a ray o !ight enters a piece o g!ass p!ate3 some it is re!ected and some reracted. I the incidence is 14 degrees3 ,hat is A0 ang!e o re!ection (0 ang!e o reraction5 The index o reraction o g!ass is 1.2 A'1 the angle of reflection is +H 0sin+H;?'41 8'1 the angle of refraction is +:H 0sin+:H;?'441'
*4 Refraction and reflection of light' 0n'd'1 Retrie!ed May +, 4?+<, from http=IIphysics'bu'eduIduffyIpy+?IReflecti on'html *: Snell5s la&' 0n'd'1 Retrie!ed May +, 4?+<, from http=II&&&'physicsclassroom'comIclassIrefr nI%essonB4ISnellBsB%a& *< (ntensity= (n!erse s7uare la&' 0n'd'1 Retrie!ed May +, 4?+<, from http=IIcsep+?'phys'ut)'eduIastr+4IlectIlightI intensity'html
