Tasks for experiments on ray optics
1. Laws of reflection and refraction
Tasks: 1. Examine the law of reflection at a plane mirror.
2. Examine the law of refraction when at a glass plate light passes over from air into
glass and from glass into air!
Preliminary considerations:
1 - Write down the equation of each the refraction and reflection law.
2 - Draw a sketch of the way of a ray of light which is reflected at the plane mirror.
3 - Name the necessary equipment and tools that you need for the experimental arrangement
of task 1.
4 - Draw a sketch of the way of the ray of light which is refracted twice when passing through
a plane parallel glass plate.
5 - Create suitable tables for data acquisition for the single subtasks. The angle of
incidence has to be increased by 5 degrees.
Apparatus and instruments:
1. experimental lamp
2. slit diaphragm
3. a semicircular glass body
4. full protractor
Implementation:
1. Prepare the experimental set-up for task 1. See picture. (extra paper)
2. Determine the corresponding reflection angle α’ for 10 incident angles α between 0° and
90°.
3. Do task 2. Change the angle of incidence by 5°. Define experimentally the corresponding
angle of reflection, first for the transition from air into glass and then from glass into air.
Note: In both tasks the incident ray shall reach the flat edge of the glass prism.
Measurement report / evaluation
1. Draw the results of task 1 in an appropriate coordinate system. Put the result into words.
2. Use the results of task 2 and calculate the refractive index of the used glass. What type of
glass could have been used?
3. While solving part 2 of task 2 a peculiarity is to be seen. Describe the observed peculiarity
and explain it.
2 Image formation at a convex lens
Tasks:
1. Determine the way of a ray in a convex lens.
2. Examine the image formation at a convex lens.
Preliminary considerations:
1. Inform about the main rays in a convex lens. Make a sketch and label a possible way in a
convex lens.
Use the following terms: optical axis, center beam, parallel beam and focus beam.
2. Draw a sketch of the experimental setup for the second task and label it. Use the terms:
Focal point, focal length, objects distance, image distance, principal rays!
3. What are real images, what are virtual images?
Apparatus and instruments:
For task 1: lamp with slit diaphragm
glass body in the shape of a convex lens
For task 2: devices of an optical bench
- 4 T-bases
- lamp
- lens with f = 100mm
- slide holder with L-slide
- transparent screen
- ruler
Implementation:
1 - Prepare the experimental setup for task 1 and draw a sketch of the beam path behind the
convex lens. For that, create with the help of the slit diaphragm a narrow and parallel as
possible light beam.
2 - Set up the experiment according to the preliminary considerations point 2. Complete the
measurement report. Use the given object distances and move the screen until a clear
image is to be seen.
Size of the
object
Object
distance g in
cm
25
20
15
10
8
Image
distance b
in cm
Image size B
in cm
Kind of image
(real/ virtual)
Position of the
image (upright/
laterally correct/
reversed)
Evaluation
1st task: Describe the path of the beams after the convex lens.
2nd task: In a partial test no picture is produced. What are the reasons of this? Explain them
with the help of the principal rays.
Examine for your results the validity of the imaging equation for lenses:
1=1 +1.
Find reasons of possible deviations.
f g b