Figure 1, shows the secular variation in the magnetic dipole moment ( M ) of the

Question

Figure 1, shows the secular variation in the magnetic dipole moment (M) of the Earth. The straight line is the best-fit to the observations.

a) Estimate from the figure the rate of change of M with time (dM/dt,).

b) How much time is needed for M to decrease to zero?

c) What do you think will happen to the geomagnetic field when M vanishes?

d) Write briefly about the consequences on life on Earth when M vanishes?

8.7 8.60ko.............. 3 8.5 X 8.3 E 8.2 D 8.1 7.9 7.8 1850 2000 1800 1900 1950 Years AD Figure 1: Secular variation trend in the Geomagnetic dipole moment.

Explanation / Answer

a)The time is plotted along x axis and dipole moment M is plotted along y axis. The rate of change of M with respect to time is dM/dt is that the dipole moment decreases as the time period increases. M and time period are inversely proportional.

b)At about 500-1000s,the value of M will entirely reach zero.

c)When M vanishes,the geomagnetic field will also slightly be affected and will decrease to some small value but not entirely zero as the earth is a natural magnet with north and south pole.

d)Earth acts as a natural magnet with north and south poles and it is said to stand on its axis which is the equator dividing it into parts. When M decreases,the magnetic stregth of earth also decreases slightly but retains some amount of magnetism in the name of residual magnetisem. The life on earth does not get affected much.

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