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General ScienceEasyAsked in: CDS · CDS-I 2025, GK

Which one among the following is used in a simple microscope?

  1. A.Diverging lens
  2. B.Concave mirror
  3. C.Converging lens
  4. D.Plane mirror

Correct answer

C. Converging lens

Explanation

The correct answer is C, Converging lens. A simple microscope is just a convex (converging) lens of short focal length, held close to the eye, which gives an enlarged image of a small object.

When the object is placed within the focal length of a convex lens, the lens forms a virtual, erect and magnified image on the same side as the object. This is how a reading glass, a watchmaker's eyepiece and a jeweller's loupe work. The shorter the focal length, the greater the magnification. A compound microscope uses two converging lenses, the objective and the eyepiece, to magnify much more.

A is wrong because a diverging (concave) lens always forms a smaller, diminished image, so it cannot magnify. B is wrong because a concave mirror can magnify, as in a shaving mirror, but a simple microscope uses a lens, not a mirror. D is wrong because a plane mirror forms an image of the same size as the object.

Exam tip: simple microscope, magnifying glass and the lens used to correct long sight (hypermetropia) are all convex lenses.

Practice Questions

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Q1.General ScienceAsked in: UPSC Civil Services · CSE Prelims 2022, GS Paper IMedium

Which of the following are nitrogen-fixing plants?

1. Alfalfa

2. Amaranth

3. Chickpea

4. Clover

5. Purslane (Kulfa)

6. Spinach

Select the correct answer using the code given below:

  1. A.1, 3 and 4 only
  2. B.1, 3, 5 and 6 only
  3. C.2, 4, 5 and 6 only
  4. D.1, 2, 4, 5 and 6
Show answer
Correct answer: A. 1, 3 and 4 only

Alfalfa, chickpea and clover are legumes, and legumes fix nitrogen. Plants of the legume family (Fabaceae) carry root nodules that house Rhizobium bacteria.

Q2.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

The mass number of an element is NOT changed when it emits

  1. A.Alpha and Beta radiations only
  2. B.Alpha and Gamma radiations only
  3. C.Beta and Gamma radiations only
  4. D.Alpha, Beta and Gamma radiations
Show answer
Correct answer: C. Beta and Gamma radiations only

Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.

Q3.General ScienceAsked in: UPSC CAPF · CAPF 2025, Paper IMedium

Which one among the following statements about facilitated transport in plants is correct?

  1. A.All passive transports are types of facilitated transport.
  2. B.Facilitated transport is an example of active transport.
  3. C.Water moves across plasma membrane by active transport.
  4. D.Facilitated transport requires assistance of carrier proteins.
Show answer
Correct answer: D. Facilitated transport requires assistance of carrier proteins.

In facilitated transport, molecules cross the membrane with the help of membrane proteins, while still moving down their concentration gradient.

Q4.General ScienceAsked in: UPSC CAPF · CAPF 2017, Paper IMedium

Who among the following has coined the term 'Quark', the fundamental particles that make up protons and neutrons in an atomic nucleus ?

  1. A.Richard Feynman
  2. B.Murray Gell-Mann
  3. C.Albert Einstein
  4. D.Niels Bohr
Show answer
Correct answer: B. Murray Gell-Mann

The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.