Astronomical telescope is used to observe a planet and final image of the planet is found to be formed at infinity. Focal length of objective lens is 20 m and that for the eyepiece is 4 cm.

Astronomical telescope is used to observe a planet and final image of

1.	Astronomical telescope is used to observe a planet and final image of the planet is found to be formed at infinity. Focal length of objective lens is 20 m and that for the eyepiece is 4 cm.
Answer» Angular magnification achieved is 500 Distance between objective and eyepiece is slightly more than 20 m. Image of the planet is inverted Aperture of objective larger than that of eyepiece Solution :Magnification for the given case is `m=(f_(0))/(f_(e))=(20)/(0.04)= 500` Hence, option (a) is correct. Length of the tube or distance between objective and eyepiece can be written as `L = f_(0) + f_(e)= 20 + 0.04 = 20.04 m` Hence, option (b) is also correct. FINALLY eyepiece forms virtual image of real image formed by objective lens and hence final image REMAINS inverted. Option (c) is also correct. In case of telescope it is required to make objective lens having larger aperture. We need sufficient amount of LIGHT from distant object to ENTER the telescope so that BRIGHTNESS of final image is OK. That is the reason we need larger aperture for objective lens. Hence option (d) is also correct. Hence all options are correct.

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Astronomical telescope is used to observe a planet and final image of the planet is found to be formed at infinity. Focal length of objective lens is 20 m and that for the eyepiece is 4 cm.

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