Test: Magnetic Field

10 Questions MCQ Test Science & Technology for UPSC CSE | Test: Magnetic Field

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What is the angle of dip at a place where the horizontal component of the earth’s magnetic field is equal to the vertical component?


The angle of dip is given by:

δ = tan−1(B​/ Bh​)

where Bv​ = vertical component of earth's magnetic field & B= horizontal components of earth's magnetic field
Here, Bv ​= Bh
► δ = tan−1(1) = 45o


How can a magnetic field be produced?


An electric current as well as the permanent magnet produces a magnetic field whereas a temporary magnet fails to do so.


Which one of the Maxwell’s laws leads to the conclusion that there are no magnetic field loops that are not closed?


Gauss’s law for magnetism states that no magnetic monopoles exist and that the total flux through a closed surface must be zero.


What is the relation between dipole moment pm, volume of bar magnet V and intensity of magnetization M? 


Magnetization is the net dipole moment aligned per unit volume.

M = p/ V


If we place a bar magnet in the magnetic meridian with its north pole towards geographic north, the neutral point will be:

  • If we place a bar magnet in the magnetic meridian with its north pole towards the geographic north, the neutral point will be on the equatorial line of the magnet.
  • If the north pole of the magnet points towards the geographical north, the fields of the magnet and the earth will point in opposite directions along the equatorial line of the magnet we get two neutral points on the equatorial line which are equidistant from the axis of the magnet.

Which combination of magnetic field lines and poles shows two magnets repelling each other?

  • The discovery that one particular pole of a magnet orients northward, whereas the other pole orients southward allowed people to identify the north and south poles of any magnet.
  • It was then noticed that the north poles of two different magnets repel each other, and likewise for the south poles. Conversely, the north pole of one magnet attracts the south pole of other magnets.
  • This situation is analogous to that of electric charge, where like charges repel and unlike charges attract. In magnets, we simply replace the charge with a pole: Like poles repel and unlike poles attract.

Magnetic field strength due to a short bar magnet on its axial line at a distance x is B. What is its value at the same distance on the equatorial line?


The magnetic field at any axial point is given by, B =  2μo/ 4πx3
Similarly, the field at any equatorial point is given by, B = μo/ 4πx3
Thus, the field at any equatorial point is half of what it is at an axial point.


When the switch is closed a magnetic field is produced by the coil. Which option shows the shape of the field?

  • The apparatus used by Faraday to demonstrate that magnetic fields can create currents is illustrated in Figure B.
  • When the switch is closed, a magnetic field is produced in the coil on the top part of the iron ring and transmitted to the coil on the bottom part of the ring.
    So, B is the correct option.

If the magnet is suspended at an angle 30° to the magnetic meridian, the dip needle makes an angle 60o with the horizontal. What is the true dip?​


Angle of dip, δ = 30º
► tanδ′ = tanδ / cosθ
► tanδ = (tan 60º) * (cos30°) = (√3) * (√3 / 2) = 3 / 2
∴ Real dip, δ′ = tan−1 (3/2)


A compass has a small balanced pointer that always points North-South. This is because:

  • A compass has a small magnet inside it with its north pole towards the tip of the needle.
  • This magnet aligns itself with the earth's magnetic field thus points towards the magnetic south and geographical north.

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