Tag: properties of a magnetic field

Questions Related to properties of a magnetic field

When a Magnetic needle is suspended freely, it always aligns itself in the direction of magnetic north and south pole of the earth, the north pole of the needle gets attracted towards the magnetic south pole of the earth and the south gets repelled equally away from it. So two equal and opposite forces acting on the needle should cancel each other which does not happen because the:

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. Force of attraction and repulsion are equal but not exactly in opposite direction

  2. Force of attraction and repulsion are not exactly equal even though in opposite direction

  3. Force of attraction and repulsion are not equal and not in opposite direction

  4. Force of attraction and repulsion are exactly equal and opposite in direction

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Correct Option: B
Explanation:

Though two equal and opposite forces are acting on the needles, they don't cancel each other as they act on two different points and they generate torque which later at proper alignment reaches equilibrium such as

$\sum F=0$ and

$\sum M=0$


The place where the angle of dip is 90 are known as

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. Geographical poles of the earth

  2. Magnetic equator

  3. Magnetic poles of the earth

  4. None of the above

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Correct Option: C
Explanation:

Angle of dip at a point on earth is the angle between earth's magnetic field at given point and the horizontal line of magnetic meridian.

Since the magnetic lines of force emerge and terminate at the poles of Earth, the magnetic lines of force at the poles are perpendicular to the surface there. Hence the angle of dip is $90^{\circ}$.

The north pole of earth's magnet is near

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. Geographic north

  2. At the center of earth

  3. Geographic south

  4. In any direction

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Correct Option: C
Explanation:

Keep this well in mind that the magnetic poles are opposite in position as the geographic poles.

Magnetic north is at geographic south and vice versa.
Geographic north is the part which includes Greenland and south is Antartica.
When we hang a bar magnet then its poles are attracted to the opposite magnetic poles of the earth. We know that opposite poles attract each other.
That's the reason why the bar's north pole turns towards the geographic north of the earth and the south to south.

The earth's field departs from its dipole shape substantially at large distance (greater than about $3000$ km). The responsible factor for this distortion is then

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. motion of ions in earth's ionosphere

  2. motion of ions in earth's atmosphere

  3. motion of ions in earth's lithosphere

  4. motion of ions in the space.

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Correct Option: A
Explanation:

Due to motion of ions in earth's ionosphere the earth's magnetic field gets modified.