An electron with a velocity of 10^7 m/s enter into a region of magnetic flux density of 0.10T, the angle between the direction of the field and the initial path of electron being 25°.Find the axial distance between two turn of the helical path

F = q v B sin Θ       describes force on the electron

F = m v^2 / R          describes force required to keep electron in circular path

q v B sin Θ = m v^2 / R

R = m v / (q B sin Θ)

R = 9.1E-31 * 1E7 / (.1 * 1.6E-19 * .423)

R = 9.1 / 6.77 * E-3 = .00134 m = .134 cm

two charges are fixed in place on the x-axis as shown. the charge at x = 0 is negative and has magnitude q = 2 μcoulombs (1 μcoulomb = 10-6 coulombs). the charge at x = d, (d = +12 cm), is positive and has magnitude q = 4 μcoulombs. find a point x = xo along the x-axis at which the electric field is zero.