positive charges

Meaning: Positive charge is one of two kinds of electric charge. A proton carries +e, where e = 1.60 × 10⁻¹⁹ C, and an object is positive when it has fewer electrons than protons. Charge is conserved and comes in whole multiples of e. Like charges repel and opposite charges attract. By convention, the electric field at a point is the direction of the force on a positive test charge, so field lines point away from positive charges.

Equation: F = kq₁q₂/r², where F is the electrostatic force (N), k = 9.0 × 10⁹ N·m²/C², q₁ and q₂ are the signed charges (C), and r is their separation (m). A positive product means repulsion; a negative product means attraction.

On the MCAT: Expect charges placed on a line or grid, with a question on the direction of the net force or field at a point by vector addition. Also tested: a positive charge accelerates along the field, moving from high to low potential, and its potential energy rises when it is pushed toward another positive charge. Conventional current is defined as the direction positive charges would move.

Common confusion: Charging an object positively removes electrons; protons stay in the nuclei. Also, the field points away from a positive source, but the force on a negative charge points opposite the field.