Refracting telescope: The angular magnification of a refracting telescope is 40 x. When the object and final image are both at infinity, the distance between the eyepiece and the objective is 143.5 cm. The telescope is used to view a distant radio tower. The real image of the tower, formed by the objective, is 6.0 mm in height. The focal point of the eyepiece is positioned at the real image. What is the focal length of the objective lens?

Question

Quizplus · Accepted Answer

The angular magnification of a telescope is given by the ratio of the focal length of the objective lens to the focal length of the eyepiece. Given the angular magnification is 40x and the distance between the eyepiece and the objective is 143.5 cm, we can find the focal length of the objective by subtracting the focal length of the eyepiece from the total length. Since the magnification is 40x, and assuming the eyepiece and objective lenses are positioned such that their focal points coincide (the distance between them equals the sum of their focal lengths), the focal length of the eyepiece is 143.5 cm / 41 (since 40 parts come from the objective and 1 part from the eyepiece in terms of magnification contribution). This calculation leads to the focal length of the objective being approximately 140 cm.

Refracting Telescope: the Angular Magnification of a Refracting Telescope Is