PASCO OS-8515C Basic Optics System - Manual (Page 14)

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B a s i c O p t i c s S y s t e m E x p e r i m e n t 3 : R e f l e c t i o n
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the incoming and the outgoing rays and mark them with arrows in the appropriate
directions.
Questions
1. What is the relationship between the angles of incidence and reflection?
2. Are the three colored rays reversed left-to-right by the plane mirror?
Part 2: Cylindrical Mirrors
T heor y
A concave cylindrical mirror focuses incoming parallel rays at its focal
point. The focal length ( f ) is the distance from the focal point to the cen-
ter of the mirror surface. The radius of curvature (R) of the mirror is
twice the focal length. See Figure 3.2.
P roced ure
1. Turn the wheel on the light source to select five parallel rays. Shine
the rays straight into the concave mirror so that the light is reflected
back toward the ray box (see Figure 3.3). Trace the surface of the
mirror and the incident and reflected rays. Indicate the incoming
and the outgoing rays with arrows in the appropriate directions.
(You can now remove the light source and mirror from the paper.)
2. The place where the five reflected rays cross each other is the focal
point of the mirror. Mark the focal point.
3. Measure the focal length from the center of the concave mirror sur-
face (where the middle ray hit the mirror) to the focal point. Record
the result in Table 3.2.
4. Use a compass to draw a circle that matches the curvature of the
mirror (you will have to make several tries with the compass set to
different widths before you find the right one). Measure the radius
of curvature and record it in Table 3.2.
5. Repeat steps 1–4 for the convex mirror. Note that in step 3, the reflected rays will
diverge, and they will not cross. Use a ruler to extend the reflected rays back
behind the mirror’s surface. The focal point is where these extended rays cross.
Q ues tions
1. What is the relationship between the focal length of a cylindrical mirror and its
radius of curvature? Do your results confirm your answer?
2. What is the radius of curvature of a plane mirror?
Table 3.2: Cylindrical Mirror Results
Concave Mirror Convex Mirror
Focal Length
Radius of Curvature
(determined using compass)
R
f
focal
point
mirror
Figure 3.2
Incident rays
Figure 3.3