D.2 Electric and magnetic fields

Objective notes

18 learning objectives

—D.2.1—Electric charge forces

• Direction of forces between the two types of electric charge.

—D.2.2—Coulomb’s law

• Coulomb’s law: F=kq1q2/r^2 for point charges; k=1/(4πε0).

—D.2.3—Charge conservation

• Conservation of electric charge.

—D.2.4—Millikan experiment

• Millikan’s experiment as evidence for quantization of electric charge.

—D.2.5—Charge transfer

• Charge transfers by friction, electrostatic induction or contact.

• Grounding can remove or add charge.

—D.2.6—Electric field strength

• Electric field strength: E=F/q.

—D.2.7—Electric field lines

• Electric field lines.

—D.2.8—Field-line density

• Relationship between field line density and field strength.

• Greater field-line density indicates stronger field.

—D.2.9—Parallel-plate field

• Uniform field between plates: E=V/d.

—D.2.10—Magnetic field lines

• Magnetic field lines.

—D.2.11 (HL)—Electric potential energy

• Electric potential energy is work to assemble charges from infinite separation.

—D.2.12 (HL)—Two-charge potential energy

• Two-charge electric potential energy: Ep=kq1q2/r.

—D.2.13 (HL)—Electric potential as scalar

• The electric potential is a scalar quantity with zero defined at infinity.

—D.2.14 (HL)—Electric potential

• Electric potential: Ve=kQ/r, zero at infinity.

—D.2.15 (HL)—Electric potential gradient

• Electric field strength is potential gradient: E=-ΔVe/Δr.

—D.2.16 (HL)—Work in electric fields

• Work moving charge in electric field: W=qΔVe.

—D.2.17 (HL)—Electric equipotentials

• Equipotential surfaces for electric fields.

• No work is done moving along an equipotential surface.

—D.2.18 (HL)—Equipotentials and electric fields

• Relationship between equipotential surfaces and electric field lines.

• Equipotential surfaces are perpendicular to electric field lines.