Physics
EM Spectrum and reflection practice
Conceptual Review
1. Consider a concave spherical mirror and an object. Is the image always inverted? Is the image
always real? Give conditions for your answers.
No, the image can be upright and virtual if the object is closer than the focal length
2. What could you do to determine if an image is real or virtual?
Try to focus the image onto a viewing screen. This can only be done with a real image.
3. What happens to a ray of light that is incident upon a concave mirror parallel to the principal
axis of the mirror?
Reflects along a line containing the focal point
4. What happens to a ray of light that passes through the focal point of a concave mirror before
being reflected?
Reflects along a line that is parallel to the principal axis
5. What happens to a ray of light that is incident upon a concave mirror along a line containing the
center of curvature?
Reflects straight back along a line containing the center of curvature
6. Which of the following does not refer to a type of electromagnetic wave?
a. radio
b. sonar
c. ultraviolet
d. X-ray
e. Microwave
f. Gamma
7. The wavelength of red light is _?_ that of blue light; the frequency of red light is _?_ that of blue
light.
a. longer than; higher than
b. shorter than; lower than
c. longer than; lower than
d. longer than; the same as
e. the same as; higher than
f. none of these
8. From lowest to highest frequency, these EM waves would be ordered
a. R-IR-UV-G
b. IR-R-UV-G
c. G-IR-UV-R
d. UV-IR-G-R
e. IR-G-R-UV
f. G-UV-IR-R
g. R-UV-G-IR
h. UV-R-IR-G
9. Construct a ray diagram for an object located between the focal point and the center of
curvature for a concave mirror:
10. Construct a ray diagram for an object located less than the focal length from a concave mirror:
11. What does negative value of focal length tell you about a mirror? The mirror is convex
12. What does a negative image distance tell you about an image? The image is virtual
13. What does the law of reflection state? Angle of incidence is equal to the angle of reflection
14. Describe how an image would change as an object is moved from very far away towards the
surface of a concave mirror.
Begins real, inverted and smaller than object…as the object is brought closer to the mirror, the
image will grow larger and further away. At the Center, the image is R, I, Same size. Between C
and F, the image will be R, I, L. When the object reaches the focal point, the image will
essentially blur out of focus at an infinite distance away. When the object is brought closer than
F, the image will be V, U, and smaller than the object.
15. Which color of the visible light portion of the electromagnetic spectrum has the highest
frequency? Most energy? Longest wavelength?
Highest f = violet, most E = violet, longest λ = red
16. What is an Electromagnetic Wave?
A self sustaining combination of vibrating electric and magnetic fields
17. Identify a potential health risk associated with exposure to…
a. Ultraviolet waves – burns, skin cancer
b. X-rays – rupture and destroy cell walls prohibiting cell function, death at high enough
exposures
Problem Solving Practice
18. The tallest man in history was 2.72 m tall. The smallest woman in history had a height of 0.55
m. Suppose the tallest man is standing 5.0 m from a converging mirror that produces an image
equal to Pauline’s height, what is the focal length of this mirror?
f = 0.84 m
19. A steel ball bearing with a radius of 1.5 cm forms an image of an object that has been placed 1.1
cm away from the bearing’s surface. Determine the image distance and magnification.
di = -0.45 cm
M = 0.41
20. The reflector of a radio telescope has a radius of curvature of 265.0 m. The radio detecting
equipment must be placed at the focal point of the reflector. How far above the reflector must
the radio-detecting equipment be placed in order to obtain clear radio images?
f = 132.5 cm
21. If a vehicle 2.0 m high is 4.6 m from a car’s convex mirror, find the position and height of the
image, given that the radius of curvature is 0.80 m.
di = -0.368 m
hi = -0.16 m
22. A thimble is 32.0 cm from a concave mirror. The focal point of the mirror is 11.0 cm. What is the
magnification of the image?
M = -0.52
23. A spherical mirror is to be used in a motion-picture projector to from an inverted, real image 95
times as tall as the picture in a single frame of file. The image is projected onto a screen 13 m
from the mirror. What type of mirror is required, and how far should it be from the film?
Concave, do =0.14 m
24. A child holds a candy bar 15.5 cm in front of a convex mirror. The image height is reduced by
one-half. What is the radius of curvature of the mirror?
R = -31.0 cm (twice the focal length)
25. Which station broadcasts with radio waves 2.94m long? Justify your answer mathematically.
A. KXPR 91.7 MHz
B. WGRD 98.5 MHz
C. KSFM 102 MHz
D. KWOD 106 MHz
E. WLAV 108 MHz
26. A child who is 1.1 m tall is standing 6.0 m from a convex mirror. The child’s image is 0.40 m
behind the mirror. What is the size of the image?
hi = 0.073 m