Pasco OS-8515C Basic Optics System Manuel d'utilisateur télécharger pdf (Page 23)

Model No. OS-8515C Experiment 8: Lensmaker’s Equation

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

and R

) 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

---

n 1–()

------

–

⎝⎠

⎜⎟

⎛⎞

Double

Concave

Lens

Incoming rays

Concave lens

Figure 8.2

1 2 ... 18 19 20 21 22 23 24 25 26 27 28 ... 70 71

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Pasco OS-8515C Basic Optics System Manuel d'utilisateur Page 23