Electric Fields


  1. The average distance between the electron and the proton in the Hydrogen atom is 5.3 x 10-11 m. How strong is the electric field the electron experiences ?

    2. |E| = k |q| / r2 = (9 x 109 x 1.6 x 10-19 )/(5.3 x 10-11)2 = 5.1 x 1011 V/m



  2. Two charges, one of +1.5 µC and the other of +3.0 µC, are 20 cm apart. Where is the electric field along the line joining them zero ?

    3. E field is given by, |E| = k |q| / r2 where r is the distance form the charge.

    Therefore, between the charges, a distance r1 from q1 and r2 from q2 the total electric field is given by

    |E| = kq1/r12 - kq2/r22

    Difference in electric fields since both charges are the same sign.

    When E= 0 we have,

    kq1/r12 = kq2/r22

    Therefore, q1/q 2 = (r1/r2)2

    but r1 + r2 = l = 0.2 m

    so that, q1/q 2 = (r1/l-r1)2

    (1.5/3) ½ = r1/(0.2-r1)

    Solving gives, r1 = 0.083 m = 8.3 cm

    That is, the location where E = 0 is 8.3 cm from the smaller charge.



  3. How strong is the electric field needed to support a proton against gravity at sea level ?

    4. Force of gravity = Electric force

    mg = qE

    E = mg/q = (1.67 x 10-27 x 9.8)/1.6 x 10-19 = 1.02 x 10-7 V/m