Questions, Further study – PASCO OS-8515C Basic Optics System User Manual

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M o d e l N o . O S - 8 5 1 5 C

E x p e r i m e n t 1 5 : T e l e s c o p e

Measure d

, the distance from the object (paper pat-

tern on screen) to the objective lens.

Determine d

, the distance from the eyepiece lens to

the image. Since the image is in the plane of the
object, this is equal to the distance between the eye-
piece lens and the object (screen). Remember that the
image distance for a virtual image is negative.

Calculate d

using d

and the focal length of the

objective lens in the Thin Lens Formula (Equation
15.1).

Calculate d

by subtracting d

from the distance

between the lenses.

Calculate the magnification using Equation 15.2.

Calculate the percent difference between the calcu-
lated magnification and the observed value.

Questions

Is the image inverted or upright?

Is the image that you see through the telescope real or virtual?

Further Study

Image Formed by the Objective Lens

Where is the image formed by the objective lens? Is it real or virtual? Use a desk lamp
to brightly illuminate the paper grid (or replace the screen with the light source’s
crossed-arrow object). Hold a sheet of paper vertically where you think the image is.
Do you see the image? Is it inverted or upright? Remove the sheet of paper and hold a
pencil in the same place. Look through eyepiece lens; you will see two images, one of
the pencil and one of the grid pattern. Are both images inverted? Use parallax to
determine the location of the pencil image.

Object at Infinity

Remove the screen and look through the lenses at a distant object. Adjust the distance
between the lenses to focus the telescope with your eye relaxed. Estimate the
observed magnification. Now calculate the magnification by taking the ratio of the
focal lengths of the lenses. Compare the calculated magnification to the observed
magnification.

How is the distance between the lenses related to their focal lengths?

Galilean Telescope

Make a new telescope using the -150 mm lens as the eyepiece and the +250 mm lens
as the objective lens. Look through it at a distant object. Adjust the distance between
the lenses to focus the telescope with your eye relaxed. How is the distance between
the lenses related to their focal lengths?

How does the image viewed through this telescope differ from that of the previous
telescope? Is the magnification positive or negative?

Table 15.1: Results

Position of Objective Lens

Position of Eyepiece Lens

Position of Screen

Observed magnification

Calculated Magnification

Percent Difference