The Electric Field
Part of the Electricity and Magnetism section of Coddy's Physics journey. Lesson 5 of 51.
The electric field at a point is the force on each coulomb of a small positive test charge there:
E = F / q
It is measured in N/C and points the way a positive charge is pushed.
Around a point charge Q:
E = k Q / r²
away from a positive charge, toward a negative one.
A charge q in a field E feels
F = q E
along E if q is positive, against it if q is negative. Field lines start on + and end on −, and they never cross.
Challenge
A small sphere carries Q = 4 μC. A tiny test charge q = 2 nC sits 0.2 m from its centre. How big is the force F on the test charge? Work out the field there first.
Try it yourself
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Electricity and Magnetism
2The Electric Field
The Electric FieldField of Several ChargesThe Uniform FieldA Charge in a Uniform FieldRecap - Stopping a Proton3Energy and Potential
Electric Potential EnergyElectric PotentialField and PotentialRecap - Accelerating Ions6Current and Resistance
Current and VoltageResistance and Ohm's LawSeries and ParallelElectric PowerRecap - Fairy Lights9Capacitors in Circuits
A Capacitor in a CircuitCharging a CapacitorDischarging a CapacitorRecap - Defibrillator