Where is the vertical component of earth's magnetic field zero?

The dip at a place is (30^0) and If the vertical component of earth's magnetic field at that point is 7.5×10^−5 T. then what will be the total magnetic field of earth at that point.

What is magnetic field?

Two rails of a railway track insulated from each other and the ground are connected to a milli voltmeter. What is the reading of millivoltmeter when the train travels at speed of 180 km/h along the track, given that the horizontal component of earth's magnetic field is 0.2*10^(-4) wb/m and the rails are separated by 1 meter.

A wheel with 25 metallic spokes each 0.4m long is rotated with a speed of 150 rev//min in a plane normal to the horizontal components of earth's magnetic field H_B at a place. If H_E=0.4G at the place, what is the induced emf between the axle and the rim of the wheel?

What are limits of earth's magnetic field?

Write about earth's magnetic field.