A negative charge is the net charge of an object with more electrons than protons; in AP Physics 2 (Topic 3.11), negative charges attract positive charges, repel other negative charges, and feel an electric force opposite the direction of the electric field.
An object has a negative charge when it carries an excess of electrons. Protons are positive, electrons are negative, and most objects have equal amounts of each, so they're neutral. Add extra electrons (or strip some away from something else) and you get a net negative charge. Charge is quantized, meaning any negative charge is a whole-number multiple of the elementary charge e, because you can't transfer half an electron.
The sign of a charge isn't just a label. It controls the direction of every electric interaction. A negative charge attracts positive charges, repels other negative charges, and feels an electric force pointing opposite to the local electric field. That last fact is the one AP Physics 2 tests relentlessly, because electric field arrows are drawn for the direction a positive test charge would be pushed. A negative charge does the opposite of what the field arrows say.
Negative charge lives in Topic 3.11 (Electric Charges and Fields), where the CED builds the foundation for everything electric in AP Physics 2: charge conservation, charging by friction/conduction/induction, Coulomb's Law, and electric fields. The sign of the charge is what makes these topics directional. Two negatives repel, a negative and a positive attract, and the magnitude of the force comes from Coulomb's Law either way. Later topics on electric potential and circuits also lean on it. Electrons (negative) are what actually move in a wire, even though conventional current is defined by positive charge flow. If you mix up what a negative charge does in a field or near another charge, you'll get force directions, trajectories, and energy changes backwards on the exam.
Keep studying AP Physics 2 Unit 3
Positive Charge (Unit 3)
Positive and negative charges are mirror images of each other. Same Coulomb's Law magnitude, opposite force direction. Whenever a problem works for a positive charge, you can solve the negative-charge version by flipping every force arrow.
Electric Field (Unit 3)
Field lines are drawn from the point of view of a positive test charge, so a negative charge feels a force opposite the field. Field lines also point toward negative charges, which is how you spot a negative source charge on a field-line diagram instantly.
Coulomb's Law (Unit 3)
Coulomb's Law gives the size of the force between two charges, and the signs tell you attract or repel. A negative times a positive gives attraction; two negatives give repulsion. The cleanest habit is to compute magnitude with absolute values, then use the signs to draw the direction.
Negative charge shows up constantly as a direction trap. The 2024 Short FRQ Q4 put a particle with mass M and charge −Q in the same setup as a positive particle and asked you to compare their motion. The whole point was recognizing that the negative particle accelerates opposite the field while the positive one accelerates with it. Multiple-choice questions love asking which way a negative charge moves in a given field, which way field lines point near a negative source charge, or whether two charges attract or repel. FRQs often combine it with energy: a negative charge gains kinetic energy moving toward higher potential, the reverse of a positive charge. Your job on any of these is the same. Track the sign, flip the direction when the charge is negative, and justify it in words ('the force on a negative charge is opposite the electric field').
A positive charge has a deficit of electrons; a negative charge has an excess. The physics confusion isn't the definition, it's the directions. A positive charge is pushed along the electric field and loses kinetic energy moving toward higher potential. A negative charge is pushed against the field and gains kinetic energy moving toward higher potential. Every direction-based answer flips when the sign flips, and that flip is exactly what FRQ comparison questions test.
A negative charge means the object has more electrons than protons, since electrons carry the negative elementary charge.
Negative charge is quantized, so any net negative charge is a whole-number multiple of the elementary charge e.
A negative charge feels an electric force opposite to the direction of the electric field, because field direction is defined by the push on a positive test charge.
Electric field lines point toward negative charges and away from positive charges.
Two negative charges repel each other, while a negative and a positive charge attract, with the force magnitude given by Coulomb's Law in both cases.
Charge is conserved, so making an object negative means electrons were transferred to it from somewhere else, leaving that other object positive.
A negative charge is the net charge of an object with an excess of electrons. It's covered in Topic 3.11, where it determines attraction, repulsion, and the direction of electric forces and fields.
No. The electric force on a negative charge points opposite to the electric field, because field direction is defined by the force on a positive test charge. This direction flip is one of the most commonly tested ideas in Unit 3.
A negative charge comes from extra electrons; a positive charge comes from missing electrons. They feel equal-magnitude Coulomb forces in a given situation, but in opposite directions, so a negative charge accelerates against the field while a positive charge accelerates with it.
No. Charge is quantized, so a net negative charge must be a whole-number multiple of the elementary charge e (about 1.6 × 10⁻¹⁹ C), because charge transfers happen one electron at a time.
Toward it. Field lines start on positive charges and end on negative charges, so on any field-line diagram, the charge the arrows converge on is the negative one.
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