REFLECTION REFRACTION OF LIGHT LABORATORY INTRODUCTION Light can
REFLECTION & REFRACTION OF LIGHT LABORATORY
INTRODUCTION Light can be reflected back into the media by mirrors and other objects. The image is formed which seems to appear behind the reflecting surface. The image is virtual because it is formed where light does not really reach. Also, the image looks exactly like the object. The law of reflection states that the angle of incidence and the angle of reflection are equal to each other. Light rays are also bend and made to change speed when they cross a boundary between two media. This is called refraction. Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal.
The angle between the incident ray and the normal is the angle of incidence. The angle between the reflected ray and the normal is the angle of reflection. The angle of incidence and angle of refraction are constantly changing based on the media. With an open kaleidoscope, we apply the concept of reflection to a mirror system with multiple reflections. Also, with simple mirrors, paper, clips and pins, we will demonstrate how to obtain the angle of incidence and the angle reflection when light from an object is reflected from a plane mirror. Using glass or plastic blocks or water, refraction of light can be demonstrated.
THE KALEIDOSCOPE
MATERIALS Viewing object (eg. Coin) Open Kaleidoscope
Procedures 1. Hold the open kaleidoscope’s two mirrors at an angle of 75º. 2. Place the object to be observed inside the angled mirrors of the open kaleidoscope apparatus. 3. Count the number of images resulting when you observe on the mirrors and record in Data Table A. 4. Reduce the angle of the mirrors by 5 degrees at a time and count the number of images at each angle. Record your findings in Date Table.
Angle Number of Images 75 4 70 4 65 4 60 5 55 6 50 6 45 8 40 8 35 10 30 12 25 14 20 18
ANALYSIS QUESTIONS 1. Explain the reasons for multiple images you observed. The reason for multiple images I observed is the angle of incidence and reflection. What I see depends on where I stand where I place the object. It occurs due to rays of light getting reflected and bounces off the opposing mirror.
2. What effect does the angle between the mirrors have on the number of the images As the angle becomes smaller, more images appear and vice versa
3. Using the information you have gained, explain the construction and operation of a kaleidoscope with three mirrors that are 60 º apart The kaleidoscope contains three mirrors with their reflecting surfaces facing one another at 60 º apart. The medium was placed between the mirrors. The result is an infinite pattern made of six symmetrical images.
REFLECTION OF LIGHT RAYS
Materials Flat mirror Clips, closed pins block or book to support the mirror in an upright position Pencil mm or cm ruler Pin
Procedures & Results 1. Take an A 4 sheet of white paper and draw a straight line across the center to divide the paper into two equal parts
2. Stand your mirror on the line drawn on the A 4 paper. The silver backing of the edge if your flat mirror should be placed on the line. The mirror should stand UPRIGHT (at right angle with a paper) and should also not be moving. The mirror should be held steady and should not move or change position during the activity
3. Draw an ‘+’ on the paper in from of the mirror slightly near one side. Stick a straight pin into the center of the ‘+’ to help line the reflection in the mirror
4. With your eye down to the level of the paper on the table, look at the image of the +/pin in the mirror. Draw a line (line X) using a ruler from the position where your eyes see the reflected image in the mirror to the point where the +/pin appears to be in the mirror. You should line up the ruler with the image seen in the mirror as if you were taking a shot on a pool table as shown below
5. Draw another line (line Y) as in step 4 while viewing the object in the mirror slight from another angle as shown below
6. Remove the mirror and the pin, and finish out the ray diagrams by extending the two lines drawn until they merge behind the line that divides the paper into two halves (where the mirror rested opposite the object as shown below). These two lines meet at the position where the image appears to be behind the mirror What is the name of the image that appears to be formed behind the mirror? Virtual image
7. Fold the paper in half along the line where the mirror was placed and look through the paper by holding up to the light. If the lines behind the mirror go through the ‘+’ object, you have done an exceptional work in positioning the mirror, ruler and drawing the lines. It should look like the picture below
8. Draw a line from the object ‘+’ to the point where line X meet the line which divides the paper into two halves where the mirror rested. At this point, draw a normal line. Use a protractor to determine the angle of incidence and angle of reflection Angle of incidence= 17º Angle of reflection= 17º Angle of incidence= 26º Angle of reflection= 26º
9. Repeat step 8 with line Y
Does your results obtained from this activity obey the law of reflection? Explain Yes, the results I obtained from this activity obey the law of reflection. The law states that the angle of incidence and the angle of reflection are equal to each other. This is proven by both line Y and X. Line X’s angle of reflection and incidence are both 17º. This angle of incidence and reflection for line Y is both 26º.
REFRACTION OF LIGHT RAYS
Materials Plastic rectangular block. Protractor Paper sheet Clips, closed pins block or book to support the mirror in an upright position Pencil mm or cm ruler Pin
Procedures & Results Observe the picture below to help you in the drawing of light rays
As the laser light passes through the block, it does not travel in a straight line. It is bent at the line drawn at right when passing through the block. The light bends toward the normal upon entering the block and away from the normal when leaving the block. Note also that some light reflection is observed where light is entering the block. The picture and diagram below represent the procedure. You are given a sheet of paper with 3 diagonal dark lines pointing toward another dark line as shown below in the right. You are to set up the block as shown.
1. Draw the line around the edge the block. 2. Get down, so your eye is at table level and view the diagonal lines through the side of your block as shown below. You should line up the ruler with the diagonal lines seen as if you were taking a shot on a pool table as shown below as done in step 4 under light reflection.
3. Line up a ruler with where the diagonal lines appear to project when looking through the side of the block and draw 3 lines to where these lines would continue as seen through your side of the block
4. Connect the lines drawn around the block to make a rectangle. 5. Also, connect the three lines drawn in step 3 to the edge of the rectangle as shown below. Label the lines as below. 6. Connect the lines through the rectangle to where the diagonal lines all meet normal to the surface on the other side of the block. Label the line zz as the Normal
7. Your drawing should look as the picture below:
8. Create a normal line for each line where it emerges from the block. Use a protractor to measure the angle of incidence and the angle of refraction when it enters inside the block and when it leaves the block. Record the angles in the table below Line 1 43 63 43 2 54 57 53 3 67 52 66. 5
Questions
How to the angles of incidence and angles of refraction when light moves out of the block compare? Explain The angles of incidence and angles of refraction when light moves out of the block is relatively the same. This is because the medium, which is the incident ray, is in the same medium of the refracted ray exiting the block it is in. In effect, they both move at equal speeds, causing them to be almost if not parallel.
(a) What direction did the rays bend as (i) they moved from air into the inside of the glass? (ii) they moved from the inside of the glass into the air? (i) They bend towards the normal (ii) They bend away the normal
Did they all bend with the same amount or some bend more? Explain The respective lines bent the same amount in itself but not the same compared to the other lines. The angle of incidence of line 1 is equal to the refracted rays angle. Same could be said for line 2 and 3. But line 1, 2, 3 bend with different angles.
Why did light bend in such a manner that you indicated? Light bend in such a manner because it moves pass through 2 different mediums with different density.
Briefly describe the process of refraction in terms of the speed of light and the changing direction of light rays In terms of speed of light we know that it is equal to C or 3 x 10^8 m/s in vaccum but it refract by different medium with different index of refraction such as water, so the speed of light will drop to 2. 25 x 10^8 m/s because the density is higher in water than in vaccum. Another example is when light is refracted by glass, the speed of light drops from 3 x 10^8 m/s to 2 x 10^8 m/s. We can conclude that light will travel slower in medium with higher density or in another word the higher refraction index.
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