1. A Crash Course in Electric Fields By Leah Chernoff

2. What are Electric Fields? What do they do? An E-field (E) exerts a force on charged particles in space. F=qE, when F is force and q is a charged particle. E-fields are created by voltage differentials between points in space. E= -∆V/R, when ∆V is the voltage difference over a certain distance R.

3. Why Does Voltage Affect the E-Field? For a point charge Q, V= kQ/R For a point charge Q, E= kQ/R 2 So, E= -dV/dr (the negative accounts for the fact that electric fields are directed in the direction opposite to the direction of increasing voltage; that is, fields go from high voltage to low voltage.)

4. Field Lines THEY CAN NEVER CROSS (like in Ghostbusters) Negative charges always feel force opposite of the electric field Double the field lines means twice as strong Positive E-field --> lines go out; lines go in for negative E-field Confused? Check out this cool simulation! http://www.vias.org/simulati ons/simusoft_efield.html http://www.vias.org/simulati ons/simusoft_efield.html

5. Example Problems There is a 10V voltage difference over 25 m. What is the magnitude of the electric field? ANSWER: E = ∆V/R; 10/25 =.4 V/m What is the force on a particle with charge -3 C in this field? ANSWER: F = qE F = -3(.4) = 1.2 N in the opposite direction of the field

6. Useful Equations and Facts Units: N/C or V/m E = -dV/dr = kQ/R 2 F = qE Another cool simulation website: http://www.its.caltech. edu/~phys1/java/phys 1/EField/EField.html http://www.its.caltech. edu/~phys1/java/phys 1/EField/EField.html