Two bar magnets oscillate in a horizontal plane in earth's magnetic field with time periods of $3\,s$ and $4\,s$ respectively. If their moments of inertia are in the ratio of $3: 2$ then the ratio of their magnetic moments will e.

Tell the proper reason for the earth’s magnetic field to occur.

The angle of dip at a place on the earth gives

The earth's magnetic field was flipped by $180^{\circ}$ a million years ago. This flip was relatively rapid and took $10^5 \,yrs$. Then, the average change in orientation per year during the flip was closest to ............ $s$

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 $18^o$. 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 $8 \times 10^{22}\; J\, T^{-1}$ 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?

A compass needle will show which one of the following directions at the earth's magnetic pole