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

1. L − l
2. L / l
3. l / L
4. L + l

Correct answer: L / l

Solution

In an astronomical telescope in normal adjustment, the magnification is given by the ratio of the length of the image formed by the eyepiece to the length of the object on the objective lens. Hence, magnification = L / l.

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