Question

If an electron is released at the equator and falls toward the earth under the influence of gravity, the magnetic force on the electron will be in what direction?

Answer 1

east = +i, North = +j and out of the page = +k

Magnetic force on a moving charge in magnetic field is given by:

F = q*VxB

q = charge on electron = -e

V = Speed of electron = V (-k) (Since given that electron is falling under the influence of gravity, So velocity will be directed into the page)

B = magnetic field of earth = B (+j) (directed north)

So,

F = -e*(-V k)x(B j)

F = e*V*B*(kxj)

In cross product: kxj = -i

F = e*V*B (-i)

-i means towards west

So force on electron will be directed towards west.

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