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General ScienceEasyAsked in: NDA · NDA-II 2023, GAT

Which one of the following statements is true for sound waves propagating in air?

  1. A.Sound is an electromagnetic wave and transverse in nature
  2. B.Sound is a mechanical wave and longitudinal in nature
  3. C.Sound is a mechanical wave and transverse in nature
  4. D.Sound is an electromagnetic wave and longitudinal in nature

Correct answer

B. Sound is a mechanical wave and longitudinal in nature

Explanation

The correct answer is B, Sound is a mechanical wave and longitudinal in nature. Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.

A sound wave in air is a series of compressions, where air particles crowd together, and rarefactions, where they spread apart. Because it depends on the particles of a medium, sound is a mechanical wave and cannot travel through a vacuum; that is why there is no sound in space. Its speed in air is about 343 metres per second at 20 degrees Celsius, faster in water and faster still in steel.

A is wrong because sound is neither electromagnetic nor transverse in air. C is wrong because sound in air is not transverse; gases cannot carry transverse waves. D is wrong because electromagnetic waves, such as light, need no medium and are always transverse.

Exam tip: sound in air, mechanical and longitudinal; light, electromagnetic and transverse.

Practice Questions

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Q2.General ScienceAsked in: NDA · NDA-II 2021, GATMedium

Imagine a current-carrying straight conductor with magnetic field of lines in anti-clockwise direction. Then the direction of current is determined by

  1. A.the Right-Hand Thumb rule and it would be in the downward direction.
  2. B.the Left-Hand Thumb rule and it would be in the downward direction.
  3. C.the Right-Hand Thumb rule and it would be in the upward direction.
  4. D.the Left-Hand Thumb rule and it would be in the upward direction.
Show answer
Correct answer: C. the Right-Hand Thumb rule and it would be in the upward direction.

For a straight wire, the right-hand thumb rule links the current to the circular field lines around it. Hold the wire in the right hand with the thumb along the current; the curled fingers then show the direction of the magnetic field lines, which form concentric circles around the wire.

Q4.General ScienceAsked in: NDA · NDA-I 2017, GATHard

Which one of the following statements is correct about the magnification of an optical microscope?

  1. A.Magnification increases with the increase in focal length of eyepiece
  2. B.Magnification increases with the increase in focal length of objective
  3. C.Magnification does not depend upon the focal length of eyepiece
  4. D.Magnification decreases with the increase in focal length of eyepiece
Show answer
Correct answer: D. Magnification decreases with the increase in focal length of eyepiece

A compound microscope magnifies more when both its lenses have short focal lengths. In a compound microscope the objective forms a real, enlarged image, and the eyepiece magnifies it further like a simple magnifier.