AP Physics 2: Algebra Based College Board

Definition and Conservation of Electric Charge

Definition and Conservation of Electric Charge

Basics of Electric Charge

• Electric charge is a fundamental property of matter. It's the property that causes matter to experience a force in an electromagnetic field.
• Particles like protons and electrons carry electric charge. Protons have a positive charge and electrons carry an equal but negative charge.
• The unit of charge in the International System of Units (SI) is the Coulomb (C).

Types of Electric Charge

• There are two types of electric charge: Positive Charge and Negative Charge.
• Like charges repel, unlike charges attract. This is known as Coulomb's Law.
• Positive Charge is carried by particles with less electrons than protons.
• Negative Charge is carried by particles with more electrons than protons.

Conservation of Electric Charge

• According to the Law of Conservation of Electric Charge, total charge in an isolated system is always conserved.
• This means that in any closed system, the sum of all electric charge remains constant.
• Charge is not created or destroyed, it simply moves from one place to another.
• In terms of circuits, the total amount of charge entering a point in a circuit must equal the total amount of charge leaving that point. This is also known as Kirchhoff’s current law.

Electric Current and Charge

• Electric current is the flow of electric charge.
• It's caused by the movement of electrons, which carry negative charge.
• In a circuit, current is measured in Amperes (A) and is calculated as the rate of flow of charge (I = Q/t, where I is current, Q is charge, and t is time).
• The direction of current is taken to be the direction in which positive charges would move. However, in reality, electrons (carrying negative charge) move in the opposite direction.

Conductors and Insulators

• Electric charge is conducted through some materials better than others.
• Conductors, like metals, allow electric charge to move freely.
• Insulators, like rubber, impede the flow of electric charge.
• A semi-conductor has properties between a conductor and an insulator. By controlling the flow of charge, semiconductors form the basis of modern electronics.

Remember, it's essential to understand the basic properties and laws governing electric charge to develop a strong foundation for more complex topics in electric circuits. Practice with calculations involving charge, current, and time, and understand their relation in a closed circuit.