Define geographic meridian. and Define magnetic meridian.

A compass needle free to turn in a horizontal plane is placed at the centre of circular coil of $30$ turns and radius $12 \;cm .$ The coil is in a vertical plane making an angle of $45^{\circ}$ with the magnetic meridian. When the current in the coil is $0.35 \;A$, the needle points west to east.

$(a)$ Determine the horizontal component of the earth's magnetic field at the location.

$(b)$ The current in the coil is reversed, and the coil is rotated about its vertical axis by an angle of $90^{\circ}$ in the anticlockwise sense looking from above. Predict the direction of the needle. Take the magnetic declination at the places to be zero.

The vertical component of earth's magnetic field is zero at or The earth's magnetic field always has a vertical component except at the

Name the elements of the earth’s magnetic field.

At which place, earth's magnetism become horizontal

At the magnetic north pole of the earth, the value of horizontal component of earth's magnetic field and angle of dip are, respectively