For IB Physics SL and HL, calculate the magnitude of the electric field between parallel plates by dividing the potential difference across the plates by their perpendicular separation:
Here, is measured in or equivalently , in volts, and in metres.
For IB Physics SL and HL, calculate the magnitude of the electric field between parallel plates by dividing the potential difference across the plates by their perpendicular separation:
Here, is measured in or equivalently , in volts, and in metres.
A pair of large, oppositely charged parallel plates produces an approximately uniform electric field between them. This means the field strength and direction are nearly constant, except close to the edges where edge effects occur.
Potential difference is the energy transferred per unit charge between two points. In a uniform field, the potential changes at a constant rate with distance, so the magnitude of the field is the potential difference per unit distance:
The electric field points from the positive plate toward the negative plate. The force on a positive test charge acts in this direction; the force on a negative charge acts in the opposite direction.
Two parallel plates have a potential difference of and are separated by .
First convert the distance to metres:
Then substitute:
Therefore, the electric field strength is , directed from the positive plate to the negative plate.
The equation assumes the plate dimensions are much larger than their separation and the point considered is away from the plate edges. If a charge is placed between the plates, its force magnitude is . For example, a positive charge in this field experiences
directed toward the negative plate.
A common misconception is to use the plate separation in centimetres. The distance must be converted to metres before substitution.
This is syllabus topic D.2 Electric and magnetic fields for both SL and HL. For a Calculate question, show the equation, unit conversion, substitution, answer, and direction if requested. Use only when the field can be treated as uniform.