Question

Questions about the eyepieces of telescopes:

A) Which of the following are functions of the eyepiece lens of a refracting telescope? (All that apply)

(a) to produce an image whose angular size is greater than that of the object

(b) to magnify the image produced by the objective lens

(c) to reverse the orientation of the image produced by the objective lens

(d) to form an image at the focal point of the objective lens

B) What must result if the eyepiece lens of a refracting telescope is replaced with a lens that has a shorter focal length? (All that apply, please)

(a) the length of the telescope must be reduced

(b) the angular magnification produced by the telescope increases

(c) the focal length of the objective lens decreases

(d) the angular size of the image seen by the viewer increases

Answer 1

A) A refracting telescope consists of two lenses. The image formed by the first lens in the telescope is used as an object for the second lens. The objective forms a real and inverted image of a object very near the focal point of the eyepiece, and this imag e formedacts as an object for the eyepiece which forms an enlarged image two. Thus the angular magnfication produced by the eyepiece will be large. Hence, options (a) and (b) are correct. B) The telescope length is given by the formula, J eyepiece Jobjective According to the question, if the length of the eyepiece decreases then the length of the telescope must be reduced for getting a good image. The angular magnification of the image is, 6-J Objective gyriece from this formula it is clear that the angular magnification increases with decreasing the focal length and the angular size increases Hence, the correct options are (a), (b), and (d)