(455) HL Important electric field equations [IB Physics HL]

Electric Field Equations Overview

• Electric fields and gravitational fields share similar equations and concepts.

Electric Potential Energy

• Definition: Work done to assemble charges from infinite separation.

• Equation: EP = K * q1 * Q2 / R or EP = K * Q (big Q, little Q) / R.

• Units:

  • EP: Joules (J)

  • K: Constant (check data booklet)

  • q1, Q2: Charges in Coulombs (C)

  • R: Distance in meters (m)

• Key Concepts:

  • EP is proportional to the product of the charges and inversely proportional to R.

  • At R = infinity, EP = 0 (no work done at infinite separation).

Electric Potential

• Definition: Work done per unit charge to bring it from infinity to a point.

• Equation: V = K * capital Q / R.

• Related Work Equation: Work = Q * ΔV.

• Units:

  • Work: Joules (J)

  • Charge: Coulombs (C)

  • Distance: Meters (m)

  • Electric potential: Volts (V)

• Conversion: 1 eV = 1.6 * 10^-19 J.

  • Relation to kinetic energy: 1 E = 1/2 m v^2 relates to energy of electrons.

Electric Field Strength

• Definition: E = V / ΔR.

• Units: Newtons per Coulomb (N/C).

Equipotential Lines

• Definition: Locations where electric potential (V) is constant.

• Equipotential lines are perpendicular to electric field lines.

• Key Concept: No work is done when moving along an equipotential line.

Charged Plates

• Electric field lines direct towards negative charge from positive charge.

• Equipotential lines are perpendicular to field lines in charged plates.

Summary of Key Equations

• Electric Potential Energy: EP = K * q1 * Q2 / R

• Electric Potential: V = K * Q / R

• Electric Field Strength: E = V / ΔR

• Work Done: Work = Q * ΔV (no work done if no change in V).

Important Distinctions

• Understand the differences between electric potential, electric potential energy, and electric field strength to avoid confusion.