Magnetic compass - class-VIII

The marked end of compass needle always points to the south pole of a magnet.

The tangent law states that if a magnetic needle is placed in two mutually perpendicular uniform magnetic fields B and H, it will come to rest at an angle theta such that B = H tan(theta).

At pole's horizontal component of earth's magnetic field is zero therefore, if needle is hold horizontally then it will stay in any position.

A freely suspended magnet rests in the geographic north-south direction.
Earth has two geographic poles, the North Pole and the South Pole. They are the places on Earth's surface that Earth's imaginary spin axis passes through. Our planet also has two magnetic poles, the North Magnetic Pole and the South Magnetic Pole just like a bar magnet. The magnetic poles are near, but not quite in the same places as, the geographic poles. The needle in a compass points towards a magnetic pole. Earth's North Magnetic Pole is actually the south pole of the Earth's geographic poles and vice-versa.
Hence, a freely suspended magnetic needle point in geographic north-south direction. The magnetic compass is the device that uses this principle. A magnetic compass contains a magnetic needle pivoted in a horizontal plane that indicates the direction of magnetic north at points on the earth's surface. It is an instrument that uses a magnetized steel bar to indicate direction relative to the earth's magnetic poles.

Statement A is false because null points are on the axial line when the north pole points north. Statement B is false because at the null point, the magnetic field of the magnet is equal and opposite to the horizontal component of the earth's magnetic field, not zero.

The north pole of the normal magnet points in the north direction of the earth. Thus by suspending a bar magnet freely, it aligns in the north-south direction.

The north end of compass needle points approximately towards north pole, which is geographic north of the earth , which is south pole of earth's magnet as per convection and attraction law.

The north pole of the normal magnet points in the north direction of the earth. Thus north direction is found first with the help of the magnet..

A freely suspended magnet always points in the north south direction as earth behaves as large magnet. the north pole of the earth's magnet attracts the south pole of the magnet and vice versa.

The compass needle acts as a freely suspended magnet which points in north-south direction under the influence of earth's magnetic field lines. So, a small plotting compass can be used to plot a magnetic field.

When a magnetic compass is brought close to a current carrying wire
there is deflection in the compass due to the formation of magnetic
field. The magnetic field lines around a long wire which carries an
electric current form concentric circles around the wire. The direction
of the magnetic field is perpendicular to the wire. 
The
deflection increases when the current is increased because the magnitude
of the field is directly proportional to the strength of the electric
current. That is, stronger the electric field, stronger the magnetic
field.

The N-pole of a compass points to the S pole of a permanent magnet. Since apposite pole always attracts.

we know,
The time period of vibration magnetometer is,
$T = 2\pi \sqrt {\dfrac{1}{{mH}}} $
For some moment of inertia $I$ and magnetic moment $m$
$T \propto \dfrac{1}{{\sqrt H }}$
T can be reduced if horizontal component of earth's magnetic field $H$ is increased. But
$H = R\cos \theta $
$H$ is high if the dip is zero.
This occurs at the equator.
Hence the period can be reduced by moving towards the equator.

Here, $H _E = 0.16G = 0.16 \times 10^{-4}T$, dip angle $(\delta) = 60^0$
Then, magnitude of earth's field.
$B _E = \dfrac{H _E}{cos \delta} = \dfrac{0.16 \times 10^{-4}}{cos 60^0} T \Rightarrow B _E = \dfrac{0.16 \times 10^{-4}}{1/2} = 0.32 \times 10^{-4}T = 0.32G$

Properties of magnetic lines of force
(i) they always start from north pole and end at the south pole of the magnet outside the magnet.
(ii) they never intersect each other.

In a compass, needle points toward earth's magnetization south thus it its tip is north and its other end is south which is repelled by south pole of other magnet.

A magnetic compass points north because all magnets have two poles, a north pole and a south pole, and the north pole of one magnet is attracted to the south pole of another magnet. 
When this magnetic compass is brought near a magnetic substance, there is change in the direction of the needle based on the polarity of the magnetic substance closer to it. Whereas for a non magnetic substance it is not so.
Hence, the direction in which a compass needle points will distinguish between a magnetic material and a non-magnetic material.

Sea water contains more dissolved salts than the drinking water. 

A compass is an extremely simple device. A magnetic compass consists of a small, lightweight magnet balanced on a nearly frictionless pivot point. No matter where you stand on Earth, you can hold a compass in your hand and it will point toward the north and south pole.