Charge

Definition

Charge is a fundamental property of matter that is the source of all electrical phenomena. It is a scalar quantity that can be positive or negative and is the basis for the attractive and repulsive forces between objects, as well as the flow of electric current.

5 Must Know Facts For Your Next Test

1. Charge can be either positive or negative, with opposite charges attracting and like charges repelling each other.
2. The SI unit of charge is the coulomb (C), which is the amount of charge that passes through a cross-section of a conductor carrying a current of one ampere for one second.
3. Charge is quantized, meaning it comes in discrete, indivisible units. The smallest unit of charge is the charge of an electron, which is approximately $-1.602 \times 10^{-19}$ C.
4. The electric dipole moment is a measure of the separation of positive and negative charges within a system, such as in an electric dipole.
5. The energy stored in a capacitor is directly proportional to the square of the charge on the capacitor and inversely proportional to the capacitance of the device.

Review Questions

• Explain how the concept of charge relates to the formation of an electric dipole.
  • An electric dipole is a system with a separation of positive and negative charges, creating a non-uniform distribution of charge. This separation of charge creates an electric dipole moment, which is a vector quantity that describes the magnitude and direction of the dipole. The electric dipole moment is directly proportional to the charge separation and is a fundamental concept in understanding the behavior of charged systems, such as in the study of electric dipoles.
• Describe how the energy stored in a capacitor is related to the charge on the capacitor.
  • The energy stored in a capacitor is directly proportional to the square of the charge on the capacitor and inversely proportional to the capacitance of the device. This relationship is expressed as $U = \frac{1}{2}CV^2 = \frac{1}{2}Q^2/C$, where $U$ is the energy stored, $C$ is the capacitance, $V$ is the voltage, and $Q$ is the charge. This demonstrates the fundamental role that charge plays in the storage of energy in a capacitive circuit.
• Analyze how the concept of charge is involved in the oscillations of an LC circuit.
  • In an LC circuit, the charge on the capacitor is constantly oscillating between the capacitor and the inductor. As the charge builds up on the capacitor, the voltage across the capacitor increases, and the energy is stored in the electric field. When the charge is maximum, the voltage is also maximum, and the energy is entirely stored in the electric field. As the charge decreases, the voltage decreases, and the energy is transferred to the magnetic field of the inductor. This continuous exchange of energy between the electric and magnetic fields, driven by the oscillation of charge, is the fundamental principle behind the oscillations in an LC circuit.

Related terms

Electric Field: The region surrounding a charged object where other charged objects experience a force. The electric field describes the strength and direction of the force acting on a test charge at any point in space.

Coulomb's Law: The physical law that describes the force of attraction or repulsion between two stationary, electrically charged objects. The force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Capacitance:

The ability of a capacitor to store an electric charge. Capacitance is determined by the physical characteristics of the capacitor, such as the area of the plates and the distance between them.