Multiple Choice Questions (MCQs): Magnetic Field - JEE MCQ

The angle of dip is given by:

δ = tan⁻¹(B_v ​/ B_h​)

where B_v​ = vertical component of earth's magnetic field & B_h = horizontal components of earth's magnetic field
Here, B_{v ​}= B_h​
► δ = tan⁻¹(1) = 45^o

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

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

Magnetization is the net dipole moment aligned per unit volume.

M = p_m / V

• 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.

• 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.

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

• 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.

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 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.