LAB: REFRACTION
Please fill the blanks for full credit.
DISCUSSION
words bank: normal, angle of refraction, incident, refracted, angle of incident, bent, refraction.
A light ray travel in a straight line from a source until it encounters some object. What happens next depends on several factors, including the nature of the material making up the object, the smoothness of the surface, and the angle at which the light ray strikes the surface. If the material is transparent, the light ray may be __________________ through the material. In these cases the light ray appears to become _________, undergoing a change in the direction of travel at the boundary between two transparent materials (such as air and water). The change of direction of a light ray at the boundary is called __________________.
Light rays traveling from a source, before they are reflected, are called_____________ rays. If an incident ray undergoes refraction, it is called a __________ ray. A line perpendicular to the surface, at the point where the incident ray strikes, is called the ____________.
The angle between an incident ray and the normal is called the ______________________________. The angle between a refracted ray and the normal is called the ______________________. These terms are descriptive in their meaning, but in each case you will need to remember that the angle is measures from a line perpendicular to the surface, the ________________.
PROCEDURE
step1: Place a clean sheet of white (unlined) paper on the cardboard. Place a glass plate approximately 5 cm square flat on the center of the paper. Use a pencil to outline the glass plate, then move the plate aside.
step2: Use a ruler to draw a straight line from the upper edge of the plate outline, making an angle of 60 degrees to the edge. Label this line IB as shown in the figure. Place one upright pin at point B immediately outside the plate outline and a second pin at point I. Return the glass plate to the outline.
step3: Bring the cardboard, and glass plate near the edge of the table so you can sight through the glass plate toward the two pins. Position a ruler so that one edge aligns with the 2 pins as shown. Draw a line along the ruler and label the line B'R. Move the glass plate aside for a second time.
step4: Draw a line B to B ' , showing the path of the light ray through the glass. Overall, the path of the light ray is from IB to BB'to B'R, showing that the light ray was bent twice.
step5: Draw normals to the surface of the glass at B and B'. Show the angle of incidence and the angle of refraction with curved arrows at both boundaries.
step6: Find the angles of incidence and refraction for both boundary. The angle are from the normals. Use a protractor.
ANALYSIS
1) Describe what happens to a light ray as it travels (a) from air to glass and (b) from glass to air.
2) Light travels faster through air than it does through glass, make a generalized statement about what happens to a light ray with respect to the normal as it moves from a faster speed in one material to a slower speed in another.
3) You will learn that there is a law (called Snell's law) that relates the angle of incidence to the angle of refraction
from air to glass: sin(i) = n sin (r). i is the angle of incidence. r is the angle of refraction. n is the index of refraction and it only depends on the medium the light has to go through. n is greater than 1. Greater n is, more bent the light will be. The index of refraction of glass is usually around 1.5. Find the index of refraction by using the first 2 columns of the TABLE1. If you did a good job, you should find a value close to 1.5.
sin(i) = n sin (r), solve for n.
4) Was the purpose of this lab accomplished? Why or why not ?
words bank: normal, angle of refraction, incident, refracted, angle of incident, bent, refraction.
A light ray travel in a straight line from a source until it encounters some object. What happens next depends on several factors, including the nature of the material making up the object, the smoothness of the surface, and the angle at which the light ray strikes the surface. If the material is transparent, the light ray may be __________________ through the material. In these cases the light ray appears to become _________, undergoing a change in the direction of travel at the boundary between two transparent materials (such as air and water). The change of direction of a light ray at the boundary is called __________________.
Light rays traveling from a source, before they are reflected, are called_____________ rays. If an incident ray undergoes refraction, it is called a __________ ray. A line perpendicular to the surface, at the point where the incident ray strikes, is called the ____________.
The angle between an incident ray and the normal is called the ______________________________. The angle between a refracted ray and the normal is called the ______________________. These terms are descriptive in their meaning, but in each case you will need to remember that the angle is measures from a line perpendicular to the surface, the ________________.
PROCEDURE
step1: Place a clean sheet of white (unlined) paper on the cardboard. Place a glass plate approximately 5 cm square flat on the center of the paper. Use a pencil to outline the glass plate, then move the plate aside.
step2: Use a ruler to draw a straight line from the upper edge of the plate outline, making an angle of 60 degrees to the edge. Label this line IB as shown in the figure. Place one upright pin at point B immediately outside the plate outline and a second pin at point I. Return the glass plate to the outline.
step3: Bring the cardboard, and glass plate near the edge of the table so you can sight through the glass plate toward the two pins. Position a ruler so that one edge aligns with the 2 pins as shown. Draw a line along the ruler and label the line B'R. Move the glass plate aside for a second time.
step4: Draw a line B to B ' , showing the path of the light ray through the glass. Overall, the path of the light ray is from IB to BB'to B'R, showing that the light ray was bent twice.
step5: Draw normals to the surface of the glass at B and B'. Show the angle of incidence and the angle of refraction with curved arrows at both boundaries.
step6: Find the angles of incidence and refraction for both boundary. The angle are from the normals. Use a protractor.
| angle of incidence 1 : air/glass | angle of refraction1 : air/glass | Angle of incidence 2: glass/air | angle of refraction 2: glass/air |
ANALYSIS
1) Describe what happens to a light ray as it travels (a) from air to glass and (b) from glass to air.
2) Light travels faster through air than it does through glass, make a generalized statement about what happens to a light ray with respect to the normal as it moves from a faster speed in one material to a slower speed in another.
3) You will learn that there is a law (called Snell's law) that relates the angle of incidence to the angle of refraction
from air to glass: sin(i) = n sin (r). i is the angle of incidence. r is the angle of refraction. n is the index of refraction and it only depends on the medium the light has to go through. n is greater than 1. Greater n is, more bent the light will be. The index of refraction of glass is usually around 1.5. Find the index of refraction by using the first 2 columns of the TABLE1. If you did a good job, you should find a value close to 1.5.
sin(i) = n sin (r), solve for n.
4) Was the purpose of this lab accomplished? Why or why not ?