Re ection and Refraction Objective Equipment List ...

1 Reflection and RefractionObjectiveIn this set of experiments, reflection and Refraction of light will be studied. For reflection, exper-iments will be done to determine if the angle of reflection is equal to the angle of incidence for abeam of light incident on a flat surface. For Refraction , Snell s Law will be ListLaser pointer, a lab-jack, an optics kit which includes: a ray table, a flat reflecting surface, and asemicircular Plexiglas lens, chalky BackgroundHow light moves through space has been a question in physics for hundreds of years. In this labexercise, light can be approximated as travelling in straight lines, or rays, from a light source. Inmoving through space, these light rays can interact with matter in two ways, a light ray shines on a smooth flat surface, then at least part of the ray will bounce off ofthe surface, or be reflected. If the angle of incidence, incident, is measured with respect to a lineperpendicular to the surface (known as thenormal), then the angle of incidence is equal to thereflected angle.

2 Incident= reflected.(1)Figure 1 illustrates this 1: Reflection from a flat surface2 Reflection and RefractionIf light shines on a transparent material, then part of the light ray will pass through the part of the ray that passes into the material is bent orrefracted. This bending, or change inthe direction of the ray occurs only at the interface between the two materials. The interaction ofthe light with the transparent material changes the speed of light as it passes through the relationship between the speed of light in a vacuumcand the speed of light in the materialvis known as the index of refractionn. The index of Refraction is defined in the following equation:n=cv.(2)This speed change causes the light ray to 2 can be used to find a relationship between the angle of the incident wave, stillmeasured with respect to the normal, and the angle of the light ray as it moves through this secondmaterial, known as the angle of Refraction .

3 This new relationship is known as Snell s Law, statedmathematically in the following equation:nisin i=nrsin r.(3)In this equation,niis the index of Refraction of the medium the incident ray is moving through, iisthe incident angle,nris the index of Refraction of the medium the refracted ray is moving through,and ris the angle of Refraction . Figure 2 illustrates the relationship between the 2: Refraction through a materialIn Figure 2, it has been assumed thatnris larger thanniso that the refracted ray is deflectedtoward the normal. If the incident medium has the larger index of Refraction , then the refracted raywill be deflected away from the normal. In this case, if the angle of incidence is large enough, therefracted ray will be bent through an angle equal to, or larger than, 90 so that the ray will remaininside the material. This is known astotal internal reflection, and is the basis for fiber optics usedin Snell s law, the minimum, or critical, angle for total internal reflection can be found bysetting the refracted angle, rin Equation 3, to 90 so that thesin(90 ) is one.

4 Substituting thisinto the Equation 3, we get the following:nisin( critical) =nr.(4)v:S08 Reflection and Refraction3In this equation,niis the index of Refraction of the incident medium,nris the index of refractionof the Refraction medium, and criticalis the critical angle for total internal will test these relationships in this set of experiments using a laser pointer as the source ofthe light Note:Be careful not to look directly into the laser beam!! You may damage your eye if youlook directly in to the laser!! Do not shine the laser pointer at anyone!! Also be sure to turn off thelaser pointer when not in Screw off the end of the laser pointer and insert the batteries, if they are not already in thelaser pointer. If the laser pointer does not come on when the button switch is pressed, tryreversing the polarity of the Place the wood platform on the lab jack. Place the ray table ( the white circular diskmarked out in degrees) on the wooden platform so that the zero degree mark is pointingtoward the laser.

5 Adjust the height of the lab jack so that the reflected ray grazes the Adjust the position of the lab jack, wooden platform, and ray table so that the laser beampasses directly along the middle of the Take the silver colored triangular piece marked Ray Optics Mirror and place it on the tiltedplatform so that the flat mirrored face aligns with the line that crosses the middle of theplatform and the zero degree mark is perpendicular to the mirror Turn the ray table to the right until the incident ray from the laser skims along the 10 this angle on your data sheet as the angle of incidence of the beam, Record the reflected angle as reflect[right] on your data Repeat steps 5 and 6 collecting data for angles 20 , 30 and 40 .8. Repeat steps 5 through 7, only now measure the incident angle from the left side of the zeroline. Record the reflected angles as reflect[left].

6 When completed, you should have two anglesof reflection for each angle of incidence; a right and left reflected angle corresponding to eachincident :S084 Reflection and RefractionRefractionRefraction in AirSimple Refraction1. If necessary re-adjust the position of the lab jack, wooden platform and the ray table so thatthe laser ray skims along the zero degree line of the ray Place the clear, semicircular plastic piece labelled cylindrical lens on the ray table so thatthe rounded portion faces away from the laser beam. Center the lens on the platform usingthe scale that runs through the center of the platform. The lens position is the Turn the ray table until the incident laser ray skims the 10 mark. Record the angle of therefracted ray ( the ray leaving the cylindrical lens), r[right], on your data sheet. Therefracted ray is due to the laser being bent as it enters the cylindrical lens.

7 Note that, sincethe laser ray travels along the radius of the cylindrical lens while it is inside the lens, the rayisnotrefracted when it leaves the cylindrical lens. If you are unsure of how to measure this,please consult your lab Repeat step 3 collecting data for angles 20 , 30 , 40 and 50 recording the refracted angle as r[right] on your data Repeat steps 3 and 4, only now measure the incident angle from the left side of the zero the refracted angle as r[left]. When completed, you should have two sets of incidentand refracted angles, one set for the left side and the other for the right Internal Reflection1. If necessary, re-adjust the position of the lab jack, wooden platform and the ray table so thatthe laser ray skims along the zero degree Re-center the cylindrical lens so that the circular part now faces the laser pointer. The opticalbench and platform should still be aligned so that the refracted and reflected beam aligns withthe zero Turn the platform to the right until the refracted ray is no longer visible on the this occurs, record the angle as critical[right].

8 This angle is the critical angle of totalinternal Turn the platform to the left, using the same procedure to find the critical angle from theleft. Record this angle as critical[left] on your data :S08 Reflection and Refraction5 Refraction in WaterSimple Refraction1. If necessary, re-adjust the position of the lab jack, wooden platform and the ray table so thatthe laser ray skims along the zero degree Fill the dish at your station with chalky water (a large beaker of chalky water should be inthe front of the lab room). Place the dish on top of the ray table, and center the dish. Adjustthe height of the lab jack so that the scattered light of the laser beam is visible through thewater. Align the visible beam with the zero marking on the ray Place the cylindrical lens in the water on the ray table so that the round portion faces awayfrom the laser. Center the lens on the platform using the scale that runs through the centerof the platform as was done in the previous Rotate the ray table to the right to set the angle of incidence at 20.

9 Record the incidentangle, i[right] and the refracted angle, r[right].5. Repeat step 4 collecting data for angles 30 , 40 , 50 and 60 . Record the refracted angle as ref lect[right].6. Repeat steps 4 and 5, only now measure the incident angle from the left side of the zero the incident angles i[left], and the refracted angles r[left] on your data Internal Reflection1. If necessary, re-adjust the position of the lab jack, wooden platform and the ray table so thatthe laser ray skims along the zero degree Re-center the cylindrical lens so that the circular part faces the laser Turn the platform to the right until the refracted ray is no longer visible on the this occurs, record the angle as critical[right]. This angle is the critical angle of totalinternal Turning the platform to the left, use the above procedure to find the critical angle from theleft. Record this angle as critical[left].

10 5. Estimate and record the uncertainty in all the angle measurements. Record the smallestmeasured angle, and calculate the percent uncertainty of the angle measurements, whichwould also be the largest percent uncertainty in the 100 measurement uncertaintysmallest measured value(5) the batteries from the laser pointer when the experiment has been :S086 Reflection and RefractionData AnalysisReflection1. For each angle of incidence, average the right reflected angle with the left reflected angle toobtain the average reflected angle, reflect[ave]. Record this value on your data For each angle of incidence, calculate the percent difference in the average reflected angle fromthe angle of incidence using the following equation:%difference= i reflect[ave] i.(6)RefractionRefraction in AirSimple Refraction1. For each angle of incidence, average the two sets of refracted angles, r[left] and r[right], toobtain the average refracted angles, reflect[ave].