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M o d e l N o . O S - 8 5 1 5 B
E x p e r i m e n t 8 : L e n s m a k e r ’ s E q u a t i o n
21
Experiment 8: Lensmaker’s Equation
Purpose
In this experiment you will determine the focal length of a concave lens in two ways:
a)
by direct measurement using ray tracing and
b)
by measuring the radius of curva-
ture and using the lensmaker’s equation.
Theory
The lensmaker’s equation is used to calculate the focal length (in air or a vacuum),
f
,
of a lens based on the radii of curvature of its surfaces (
R
1
and
R
2
) and the index of
refraction (
n)
of the lens material:
(eq. 8.1)
In this notation,
R
is positive for a convex surface (as viewed from outside the lens)
and
R
is negative for a concave surface (as in Figure 8.1).
Figure 8.1
Procedure
1.
Place the light source in ray-box mode on a white sheet of paper. Turn the wheel
to select three parallel rays. Shine the rays straight into the convex lens (see Fig-
ure 8.2).
Note: The lens has one flat edge. Place the flat edge on the paper so the lens stands stably
without rocking.
Required Equipment from Basic Optics System
Light Source
Concave Lens from Ray Optics Kit
Other Required Equipment
Metric ruler
1
f
---
n
1
–
(
)
1
R
1
------
1
R
2
------
–
⎝
⎠
⎜
⎟
⎛
⎞
=
Double
Concave
Lens
R
2
R
1
Incoming rays
Concave lens
Figure 8.2
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 ...