Q24. A Galilean telescope has fₒ = +90 cm and fₑ = -10 cm. With final image at infinity, its angular magnification magnitude, image orientation and tube length are:
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Q24. A Galilean telescope has fₒ = +90 cm and fₑ = −10 cm. With final image at infinity, its angular magnification magnitude, image orientation and tube length are:

G1 Physics · Accepted Answer

GIVEN: Galilean telescope fₒ = +90 cm and fₑ = −10 cm; final image at ∞. Step 1: A Galilean telescope uses a concave eyepiece, so its front-focus arrangement gives L = fₒ − |fₑ|. Step 2: L = 90 − 10 = 80 cm. Step 3: Angular magnification (with orientation sign) M = −fₒ/fₑ = −90/(−10) = +9. Step 4: Positive angular magnification means the final image is erect. FINAL ANSWER: 9, erect, 80 cm. Option A.