The Reflection of Light
SPH 3U
You have previously studied the reflection of light - although it may have been about 4 years
ago! To review, go to this website and read through the tutorial. Try the interactive quizzes “
Check your Understanding”. Ultimately, you will be responsible for Lessons 1 to 4 (all of
them) on this website. This corresponds with Chapter 10 in Physics 11.
Go to this website: http://www.physicsclassroom.com/Class/refln/
Now, test yourself with these problems:
Questions 1 - 7 may require that you find out what a pinhole camera is - try a websearch.
1.
Calculate the distance from the pinhole to an object that is 3.5 m high, and whose image
is 10 cm high in a pinhole camera 20 cm long.
2.
Calculate the height of a building 300 m away from the pinhole that produces an image
3.0 cm high in a pinhole camera 5.0 cm long.
3.
A 1.5 cm inverted image is produced on the screen of a camera when a picture is taken
of an 80 m tall tree. What is the magnification?
4,
A pinhole camera 25 cm long is used to photograph a building 10m high located 30 m
from the camera. Calculate the height of the image on the film.
5.
A pinhole camera 20.0 cm long is used to photograph a student 175 cm high. If the
image is 10.0 cm high, how far from the camera is the student?
6.
Determine the magnification in each of questions 4 and 5.
7.
A large pinhole camera has a magnification of 0.050 for a tree located 5.0 m from the
camera. What is the size of the image on the screen?
8.
A point object is located a perpendicular distance of 3.0 cm from a plane mirror.
(a) Using a full-scale diagram, locate the virtual image.
(b) Place an eye 2.0 cm to the left of the object. Using a ray diagram, show how the eye
"sees" the image.
Questions 8 - 12 can be considered Communications questions.
8.
In a plane mirror, where is the image?
9.
Since the image cannot be put on a screen, what type of image is it that is formed behind
a plane mirror?
10. What are the three characteristics of an image in a plane mirror?
11. Although the image in a plane mirror is not inverted vertically, relative to the object, it has
been changed. How?
12. You are given the position of an object relative to a plane mirror. List the steps you would
follow to locate the image behind the mirror.
13. What is the angle of incidence when there is an angle of 60° between the incident rays
and the reflected rays?
14. The Laws of Reflection apply not only to light but also in mechanics. Transfer the
diagram to your notebook and show how to aim billiard ball A (with no spin) so that it will
hit ball C without hitting ball B.
15. In this diagram, which eye(s) would see the image in the mirror?
16. A ray of light falls on a plane mirror. The mirror is turned through 5°. The reflected ray is
found to have turned through 10°. Explain.
17. An object 4 cm high is located 15 cm in front of a plane mirror. What are the
characteristics and the location of the image?
18. A student stands 3.0 m in front of a plane mirror.
(a) How far behind the mirror is her virtual image?
(b) If she steps forward 1.0 m, what distance will separate her from her virtual image?
19. A student sitting in an optician's chair views a chart located 1.0 m behind his head by
facing a mirror 2.5 m away from him. How far from him does the chart appear to be?
20. You can look into a mirror 10 cm wide and see reflected in the mirror the entire width of
the room, which may be 5 m wide. Explain how this is possible.
21. A girl is 1.5 m tall and stands 2.4 m in front of a vertical mirror. For the mirror to be of
minimum length, the light reflected from the girl's shoes should be reflected to the girl's
eyes from the bottom of the mirror. If the girl's eyes are located a vertical distance of 12
cm from the top of her head, and she is able to see her entire body in the mirror, what will
be:
(a) the minimum length of the mirror?
(b) the distance from the bottom of the mirror to the floor?
22. Trace the diagram below into your notebook.
(a) Indicate the location of four of the virtual images formed by the two mirrors.
(b) With separate ray diagrams, show how the eye "sees" each of the multiple images.
Selected answers
1.
2.
3.
4.
5.
7.0 m
2
1.8 x 10 cm
-4
1.9 x 10
8.3 cm
350 cm
6.
7.
18.
19.
21.
3
-2
8.3 x 10- , 5.7 X 10
2.5 cm
(a) 3.0 m (b) 4.0 rn from the image
6.0 m
(a) 0.75 m (b) 0.75 m