®
M o d e l N o . O S - 8 5 1 5 B
T e a c h e r ’ s G u i d e
49
Experiment 6: Convex and Concave Lenses
Typical results:
(Step 5)
When the lenses are nested together, parallel rays entering the lenses emerge nearly parallel; this tells us
that the focal lengths are of approximately equal magnitude and opposite sign.
(Step 6)
By moving the lenses
apart, the spacing of the rays can be changed, but they remain nearly parallel.
Typical results:
Answers to questions:
1.
A plano-convex lens is converging when it has a higher index of refraction than
the surrounding medium. It is diverging when it has a lower index of refraction.
2.
It is
not
possible to predict
whether a plano-concave lens of unknown material will be diverging or converging under water because its index
of refraction may be less than
or
greater than that of water.
Experiment 8: Lensmaker’s Equation
Typical results:
(Step 3)
Measured focal length:
f
=
−
12.0 cm
(Step 4)
Measured focal distance of reflected rays: R/2 = 6.0 cm. Radius of curvature: R =
−
12.0 cm
(Step 5)
Calculated focal length:
(Step 6)
% Difference: 0.8%
The actual radius of curvature or the lens is about
−
12.7 cm.
Convex Lens
Concave Lens
Focal Length
13.75 cm
-12.1 cm
Table 7.1: Predictions and Observations
Lens
surrounded by:
Section 1
filled with:
Section 2
filled with:
Section 3
filled with:
Prediction
(converging or diverging)
Observation
(converging or diverging)
Air
Water
Air
Air
diverging
Air
Water
Air
converging
Air
Air
Water
converging
Water
Air
Water
diverging
Water
Air
Water
Water
converging
Water
Air
Water
diverging
Water
Water
Air
diverging
f
n
1
–
(
)
1
R
⁄
1
R
⁄
+
(
)
[
]
1
–
1.5
1
–
(
)
1
12.0
–
cm
(
)
⁄
1
12.0
–
cm
(
)
⁄
+
(
)
[
]
1
–
12.1 cm
–
=
=
=
Summary of Contents for OS-8515B
Page 6: ... Basic Optics System About the Experiments 6 ...
Page 26: ... Basic Optics System Experiment 9 Apparent Depth 26 ...
Page 38: ... Basic Optics System Experiment 13 Telescope 38 ...
Page 42: ... Basic Optics System Experiment 14 Microscope 42 ...
Page 44: ... Basic Optics System Experiment 15 Shadows 44 ...
Page 46: ... Basic Optics System Telescope and Microscope Test Pattern 46 ...