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General ScienceMediumAsked in: NDA · NDA-II 2019, GAT

Which one of the following statements regarding lenses is not correct?

  1. A.A convex lens produces both real and virtual images.
  2. B.A concave lens produces both real and virtual images.
  3. C.A convex lens can produce images equal, greater and smaller than the size of the object.
  4. D.A concave lens always produces images smaller than the size of the object.

Correct answer

B. A concave lens produces both real and virtual images.

Explanation

The correct answer is B, A concave lens produces both real and virtual images. For a real object, a concave lens always forms a virtual image, so this statement is wrong.

A concave lens is a diverging lens: it spreads out parallel rays so that they seem to come from its focus on the same side as the object. Wherever the object is placed, the image is virtual, erect, diminished and formed between the focus and the lens. A convex lens is a converging lens, and its image changes with the object's position. Beyond the focus it gives real, inverted images, and within the focus it gives a virtual, erect, magnified image, which is how a magnifying glass works.

A is correct: a convex lens gives real images beyond the focus and a virtual image within it.

C is correct: a convex lens gives an image of the same size at 2F, larger between F and 2F, and smaller beyond 2F.

D is correct: the image formed by a concave lens is always diminished.

Exam tip: concave lens, always virtual, erect and diminished; object at 2F of a convex lens, image same size at 2F.

Practice Questions

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Q1.General ScienceAsked in: UPSC CAPF · CAPF 2019, Paper IMedium

The principle involved in paper chromatography is

  1. A.Absorption
  2. B.Partition
  3. C.Solubility
  4. D.Volatility
Show answer
Correct answer: B. Partition

Paper chromatography separates substances because each one divides, or partitions, itself differently between two liquid phases. In paper chromatography the stationary phase is the water held in the cellulose fibres of the paper, and the mobile phase is the solvent that rises up the paper by capillary action.

Q3.General ScienceAsked in: UPSC CAPF · CAPF 2019, Paper IEasy

Which one of the following is NOT a luminous object ?

  1. A.Sun
  2. B.Electric lamp
  3. C.Candle
  4. D.Moon
Show answer
Correct answer: D. Moon

The Moon gives out no light of its own; it only reflects sunlight, so it is a non-luminous object. A luminous object produces and emits its own light, while a non-luminous object is seen only because it reflects light falling on it.

Q4.General ScienceAsked in: UPSC CAPF · CAPF 2023, Paper IMedium

In experiment #1, a bar magnet is moved towards a conducting wire loop axially, with the magnet's north pole facing the loop. In experiment #2, the same process as in experiment #1 is repeated except that the south pole of the magnet faces the loop. Which one of the following statements is true in this context?

  1. A.The direction of current in the loop will be of opposite nature in both the experiments.
  2. B.The direction of current in the loop will be the same in both the experiments.
  3. C.No current will flow in either of the two experiments.
  4. D.More current will flow in the loop in experiment #1.
Show answer
Correct answer: A. The direction of current in the loop will be of opposite nature in both the experiments.

Reversing the pole that approaches the loop reverses the change in magnetic flux, so the induced current reverses too. When a magnet moves towards a closed loop, the magnetic flux through the loop changes and an electric current is induced (Faraday's law of electromagnetic induction).

Q5.General ScienceAsked in: NDA · NDA-I 2018, GATMedium

Which one of the following statements about classification of plants is correct?

  1. A.Thallophytes have well differentiated body design
  2. B.Funaria is a fungus
  3. C.All Pteridophytes are Phanerogams
  4. D.Vascular system is not found among Bryophytes
Show answer
Correct answer: D. Vascular system is not found among Bryophytes

Mosses and liverworts have no xylem or phloem, so water moves through them cell to cell. Bryophytes, such as Funaria (a moss) and Marchantia (a liverwort), are called the amphibians of the plant kingdom because they live on land but need water for fertilisation.