Electric Fields

Mass distorts the space-time around it creating a gravitational field of different strengths depending how far you are away from the mass.

Electric charges do the same thing Electric charges do the same thing. An electric field is created around the charge, whose strength is defined as: Charge of small, + test charge The units would be N/C

Electric field strength can also be related in terms of charge and distance from that charge: Amount of charge Electric field strength Distance2 from charge Coulomb’s Constant

In talking about an electric field, you decide what a small, positive “test charge” would do, when talking about the direction of forces.

Electric field lines show the direction of force on a positive test charge The concentration of field lines represents the strength Field lines cannot cross

Find the Electric Field strength here EB= kCq/r2 = (8.99 x 109 Nm2/C2)(8.9 x 10-6C)/(4m)2 = 5001 N/C 5001 N/C EA = (8.99 x 109 Nm2/C2)(5.8 x 10-6C)/ (5m)2 EA = 2086 N/C Resultant = ((5001 N/C)2 + (2086 N/C)2)-1/2 2086 N/C = 5418 N/C Direction = tan-1 (2086 N/C)/(5001 N/C) = 270° + 23° = 293°

Equilibrium

Problem 1 An electron is suspended 10 m above another electron, and dropped. At what point will the dropped electron float motionless in space? me = 9.109 x 10-31 kg qe = 1.60 x 10-19 C Fg = FE kC = 8.99 x 109 Nm2/C2 g = -9.81 m/s2 = 5.075 m

Problem 2 A charge of 3mC is 10m away from a charge of 7mC. Where would a charge of -5mC, placed between them, be motionless? x = ? q3 = -5 x 10-3 C q2 = 7 x 10-3 C q1 = 3 x 10-3 C F13 = F23

= 3.95m