Answer the following questions regarding earth's magnetism.
a. A vector needs three quantities conventionally used to specify the earth's magnetic field.
b. The angle of dip at a location in southern India is about `18^@` . Would you expect a greater or smaller dip angle in Britain ?
c. If you made a map of magnetic field lines at Melboune in Australia, would the lines seem to go into the groung 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 xx10^(22)JT^(-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 ?

Explanation

a. Magnetic elements
i. declination `" "` ii. Dip and `" "` horizontal intensity.
b. Greater in Britain (it is about `70^@` ) , because Britain is closer to the magnetic north pole
c. Field lines of B due to the earth.s magnetism would seem to come out of the ground.
d. Compass needle can move only in horizontal plane. Since field is entirely vertical no directions is shown by the needle.
e. Calculate B , from `B=(mu_0M)/(4pir^3),M=8xx10^(22)JT^(-1)`
`r=6.4xx10^6m` . It turns to the value `~~0.3G` approximately the horizontal field as the surface.
f. Because of the deposit of magnetic , at different places, there can be different local poles.