Skip to content
GK24
Prime
General ScienceEasyAsked in: NDA · NDA-I 2024, GAT

Which one of the following is primarily responsible for conduction of current in a metal?

  1. A.Bound electrons
  2. B.Free electrons
  3. C.Both bound and free electrons
  4. D.Ions

Correct answer

B. Free electrons

Explanation

The correct answer is B, Free electrons. In a metal, the outer electrons of the atoms are not tied to any one atom and drift through the lattice when a voltage is applied, carrying the current.

Metal atoms give up their valence electrons to a common pool, often described as a sea of electrons around fixed positive ions. These free or conduction electrons move randomly at high speed, and an electric field gives them a slow drift in one direction, which is the electric current. The large number of free electrons also explains why metals conduct heat well and look shiny.

A is wrong because bound electrons are held tightly in inner shells and cannot move through the metal. C is wrong because bound electrons do not take part in conduction. D is wrong because the positive ions in a metal stay fixed in the crystal lattice; ions carry current in electrolytes, not in metals.

Exam tip: metals conduct by free electrons, electrolytes by ions, semiconductors by electrons and holes.

Practice Questions

View all
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.

Q3.General ScienceAsked in: NDA · NDA-II 2023, GATEasy

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
Show answer
Correct answer: 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.

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.