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(A) For a Cassegrain telescope, the primary mirror is a concave mirror with radius of curvature $R_1 = 25 \ cm$, so its focal length $f_1 = R_1/2 = 12

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$40 \ cm$ from convex mirror

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(A) For a Cassegrain telescope, the primary mirror is a concave mirror with radius of curvature $R_1 = 25 \ cm$, so its focal length $f_1 = R_1/2 = 12.5 \ cm$.The secondary mirror is a convex mirror with radius of curvature $R_2 = 16 \ cm$, so its focal length $f_2 = R_2/2 = 8 \ cm$.Light from an object at infinity strikes the primary mirror and would form an image at its focus, $12.5 \ cm$ behind the mirror.However, the secondary mirror is placed at a distance $d = 2.5 \ cm$ from the primary mirror.The distance of the virtual object for the secondary mirror from the secondary mirror is $u = 12.5 - 2.5 = 10 \ cm$.Using the mirror formula for the secondary mirror: $1/v + 1/u = 1/f$.Here, $f = +8 \ cm$ (convex mirror) and $u = +10 \ cm$ (virtual object).$1/v + 1/10 = 1/8 \implies 1/v = 1/8 - 1/10 = (5-4)/40 = 1/40$.Thus, $v = 40 \ cm$.The image is formed $40 \ cm$ from the convex mirror.

$A$ Cassegrain telescope uses two mirrors of radii of curvature $25 \ cm$ and $16 \ cm$ separated by a distance of $2.5 \ cm$. The position of the final image of an object at infinity is

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