In an astronomical telescope in normal adjustment, a straight black line of length L is drawn on the inside part of objective lens. The eyepiece forms a real image of this line. The length of this image is l. Then magnification of the telescope is:
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Question

In an astronomical telescope in normal adjustment, a straight black line of length L is drawn on the inside part of objective lens. The eyepiece forms a real image of this line. The length of this image is l. Then magnification of the telescope is:

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G1 Physics · Accepted Answer

Step 1: The telescope angular magnification is M = fₒ/fₑ. Step 2: The black line is in the plane of the objective; the eyepiece images that object plane with lateral magnification related to lens separation fₒ + fₑ. Step 3: For this imaging arrangement, the measured transverse scale gives M = L/l (as indicated by the diagram). Final answer: (D) L/l; the exact optical geometry is in the printed diagram.