A microscope may be a combination of :
- A.two convex lenses.
- B.a convex and a concave lens.
- C.two concave lenses.
- D.a convex lens and a convex mirror.
Correct answer
Explanation
The correct answer is A, two convex lenses. A compound microscope uses two converging lenses, the objective and the eyepiece, to give a greatly magnified image of a tiny object.
The objective lens has a very short focal length and sits close to the object; it forms a real, inverted and magnified image inside the tube. The eyepiece, also convex, acts like a magnifying glass and enlarges that image further into a virtual image seen by the eye. The total magnification is the product of the two lenses' magnifications. A simple microscope is just a single convex lens used as a magnifier.
B is wrong because a convex objective with a concave eyepiece is the Galilean telescope, not a microscope. C is wrong because two concave lenses only spread light and cannot form a magnified real image. D is wrong because a convex mirror always forms small images, as in a vehicle's rear-view mirror.
Exam tip: microscope and astronomical telescope both use two convex lenses; the microscope's objective has the shorter focal length.
Practice Questions
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- B.Thomas Newcomen
- C.James Watt
- D.Richard Arkwright
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- B.10 Ω
- C.5 Ω
- D.15 Ω
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- B.nearby object is focused before the retina.
- C.distant object is focused before the retina.
- D.distant object is focused beyond the retina.
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- B.By evaporation
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- B.nose
- C.ear
- D.urinary bladder
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