A Charge in a Uniform Field
Part of the Electricity and Magnetism section of Coddy's Physics journey. Lesson 8 of 51.
In a uniform field a charge feels a constant force F = q E, so it has a constant acceleration:
a = q E / m
along E for a positive charge, against E for a negative one.
For an electron or a proton the weight is tiny next to the electric force and is left out. A heavier charged drop can hang still when q E = m g.
A charge entering sideways keeps its speed across the field and speeds up along it: it moves on a parabola.
Challenge
A tiny oil drop of mass 4.8 × 10⁻¹⁵ kg carries a positive charge of 3.2 × 10⁻¹⁹ C. It hangs still between two horizontal plates. How strong is the field E between the plates?
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