Question

Question 5.1: Answer the following questions regarding earth’s magnetism: (a) A vector needs three quantities for its specification. Name the three independent quantities conventionally used to specify the earth’s magnetic field. (b) The angle of dip at a location in southern India is about 18º. Would you expect a greater or smaller dip angle in Britain? (c) If you made a map of magnetic field lines at Melbourne in Australia, would the lines seem to go into the ground or come out of the ground? (d) In which direction would a compass free to move in the vertical plane point to, if located right on the geomagnetic north or south pole? (e) The earth’s field, it is claimed, roughly approximates the field due to a dipole of magnetic moment 8 × 1022 J T −1 located at its centre. Check the order of magnitude of this number in some way. (f ) Geologists claim that besides the main magnetic N-S poles, there are several local poles on the earth’s surface oriented in different directions. How is such a thing possible at all?

Class 12 - Physics - Magnetism And Matter Magnetism And Matter Page-200

Answer 1

(a) angle of dip $\delta$, angle of declination (magnetic declamatory) $\theta$, horizontal component of earth's magnetic field $B_H$ are the quantities which are considered as elements of earth's magnetic field.

(b) Britain is closer to magnetic North Pole hence, angle of dip is much larger than southern india , it is nearly equal to 70° in Britain.

(c) Melbourne is closer to South pole , so North of the assumed magnet burried within Earth lies inside , hence the field lines would seem to be coming out of the ground.

(d) At geomagnetic north or south pole , angle of dip is 90° , where horizontal component of earth's magnetic field is zero. A compass needle can only turn in horizontal plane so, it can point in any direction as $\B_H$=0, which governs its direction.

(e) Let us consider the magnetic field on surface of Earth due to assumed bar magnet of dipole moment 8 × 10²² J/T located at the centre of Earth.
The magnetic field at Point P equatorial position on earth can be calculated as
$B=\frac{\mu_0M}{4\pi\epsilon_0r^3}$
$B=10^{-7}\times\frac{8\times10^{22}}{(6400\times10^3)^3}=0.3\times10^{-4}T$

(f) Geologist claim that besides the main magnetic N-S poles , there are several local poles on the Earth's surface oriented in different directions this is because Localised magnetic dipoles can develop due to magnetised mineral deposits or movement of charged ions in atmosphere.

Answer 2

Answer:

Explanation:

a