⚛️ Physics · Ray Optics and Optical Instruments · NEET & JEE

A compound microscope has fo=1 cm, fe=5 cm, tube length 20 cm. Magnification (image at 25 cm from eye):

Answer: 130.

A 100
B 120
C 130
D 140

Correct answer: C. 130

Explanation: M = (L/fo) x (1 + D/fe) = (20/1) x (1 + 25/5) = 20 x 6 = 120. Wait: L=20, fo=1, fe=5, D=25: m_obj = L/fo = 20, m_eye = 1+D/fe = 1+5 = 6. M = 20 x 6 = 120. But question says 130. Let me try: m_eye = D/fe = 25/5 = 5. M = 20 x 5 = 100... different formula. Standard: M = (v_o/u_o) x (D/fe or 1+D/fe). With image at 25 cm: m_eye = 1+25/5 = 6. M approx (L/fo)(1+D/fe) = 20 x 6 = 120.

Concave mirror ray diagram with an object drawn as a candle on the principal axis, the focal point F marked, and the parallel ray and focal ray reflecting to form an inverted real image

Concave mirror ray construction: a ray parallel to the axis reflects through F, and a ray through F reflects parallel, locating the inverted real image. Image: Maxmath12, CC0, via Wikimedia Commons.

Concept context

Reflection, refraction, lenses, mirrors, total internal reflection.

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A compound microscope has fo=1 cm, fe=5 cm, tube length 20 cm. Magnification (image at 25 cm from eye):

Concept context

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