The earth's magnetic field varies from point to point in space. Does it also change with time? If so, on what time scale does it change appreciably?

How does the rate of reaction change with time.

A short bar magnet of magnetic moment 0,21 A - m^(2) is placed with its axis perpendicular to the direction of the horizontal component of the earth 's magnetic field .The distance of the point on the axis of the magnet from the centre of the magnet where the resultant magnetic field is inclined at 45^(@) with the horizontal component of the earth's field direction is (horizontal component of the earth's magnetic field 4.2xx10^(-5)

What happens if focal length of the eye lens does not change ?

The earth's magnetic field at the geometric poles is sqrt(10)xx10^(-5) T. The magnitude of the field at a point on the earth's surface where the radius makes an angle theta with the axis of earth's assumed magnetic dipole is 5xx10^(-5) T. The magnitude of theta in degree is :

A long straight horizontal cable carries a current of 2.5 A in the direction 10^(@) south of west to 10^(@) north of east. The magnetic meridian of the place happens to be 10^(@) west of the geographic meridian. The earth's magnetic field at the location is 0.33 G, and the angle of dip is zero. Locate the line of neutral points (ignore the thickness of the cable) ? (At neutral points, magnetic field due to a current-carrying cable is equal and opposite to the horizontal component of earth's magnetic field?.

A short bar magnet placed in a horizontal plane has its axis aligned along the magnetic north-south direction. Null points are found on the axis of the magnet at 14 cm from the centre of the magnet. The earth's magnetic field at the place is 0.36 G and the angle of dip is zero. What is the total magnetic field on the normal bisector of the magnet at the same distance as the null-point (i.e., 14 cm) from the centre of the magnet ? (At null points, field due to a magnet is equal and opposite to the horizontal component of earth's magnetic field.)