PASCO OS-8459 Beginning Optics System - Manual (Page 45)

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M o d e l N o . O S - 8 4 5 9 T e a c h e r ’ s G u i d e
45
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.
Experiment 7: Hollow Lens
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.
Table 6.1: Results
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 – = = =