Bissoy.com
Doctors Medicines MCQs Q&A

A magnetic needle free to rotate in three dimensions 

A magnetic needle free to rotate in three dimensions  Correct Answer always aligns itself with the net magnetic field direction at that point

CONCEPT:

Geographical and magnetic poles

  • The strength of the earth’s magnetic field varies from place to place on the earth’s surface; its value being of the order of 10–5 T. 
  • The axis of the dipole does not coincide with the axis of rotation of the earth but is presently titled by approximately 11.3° with respect to the latter. The magnetic poles are located where the magnetic field lines due to the dipole enter or leave the earth.
    • The location of the north magnetic pole (also called magnetic north) is at a latitude of 79.74° N and a longitude of 71.8° W, a place somewhere in northern Canada. The magnetic south pole (magnetic south) is at 79.74° S, 108.22° E in Antarctica.
  • The pole near the geographic north pole (also called true north) of the earth is called the north magnetic pole. Likewise, the pole near the geographic south pole is called the south magnetic pole. 
    • The north magnetic pole behaves like the south pole of a bar magnet inside the earth and vice versa. 

​

EXPLANATION:

  • Imagine a magnetic needle as a bar magnet or a current-carrying loop. Any magnet free to rotate in space aligns itself with the net magnetic field at that point. Therefore option 4 is correct.

Related Questions

If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity
A magnetized needle of the magnetic moment 20 JT-1 is placed at 60o with the direction of the uniform magnetic field of magnitude 9 T. What is the torque acting on the needle?
Which of the following statements is/are incorrect about the Prismatic Compass? A. The needle is broad but it does not act as an index. B. The graduated ring is attached with the needle. This does not rotate along with the line of sight. C. The readings are taken directly seeing through the top of the glass.
Fabric part needle of a sewing machine includes
1. Set point needle
2. Ball point needle
Select the correct answer
Fast needle method is more accurate than the free needle method.
In traversing by fast needle method, there are three methods of observing the bearings of lines by fast needle method.
A current carrying coil having magnetic moment M is placed in a magnetic field B. Initially the magnetic field is perpendicular to the plane of the coil and then coil turned about an axis such that the angle between the magnetic field and the plane of the coil become zero. Then choose the correct statement.
A line PQ in an old map had magnetic bearing of N 57° E when the local magnetic declination was 2°E. If the magnetic declination is now 4°W, what will be the magnetic bearing of the line PQ now?
In a region with magnetic declination of 2°E, the magnetic Fore bearing (FB) of a line AB was measured as N79°50’E. There was local attraction at A. TO determined the correct magnetic bearing of the line, a point O was selected at which there was no local attraction. The magnetic FB of line AO and OA were observed to be S52° 40’E and N50°20’W, respectively. What is the true FB of line AB?
Consider the following statement: a) Magnetic field lines are always form closed curve. b) Magnetic field lines start from north pole outside the magnet c) Magnetic field lines start from south pole outside the magnet Which of the following is a property of magnetic field lines?