Electric Charge and Current
1. Electric Charge
Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric and magnetic field. There are two types of electric charge: positive and negative. Like charges repel each other, while opposite charges attract.
Example: When you rub a balloon on your hair, the balloon becomes negatively charged due to the transfer of electrons from your hair. If you bring the charged balloon close to another uncharged balloon, they will attract each other because the uncharged balloon will polarize, creating a slight attraction.
2. Conductors and Insulators
Conductors are materials that allow electric charge to flow through them easily, while insulators do not. Conductors have free electrons that can move through the material, whereas insulators have tightly bound electrons that do not move easily.
Example: Metals like copper and aluminum are good conductors because they have free electrons that can move easily. On the other hand, materials like rubber and plastic are insulators because their electrons are tightly bound and do not move easily.
3. Electric Current
Electric current is the flow of electric charge through a conductor. It is measured in amperes (A) and represents the amount of charge passing through a point per unit time. Current can be direct (DC) or alternating (AC), depending on the direction of the flow of charge.
Example: When you turn on a light bulb, electric current flows from the battery through the wires to the bulb, causing it to light up. The current is direct if the charge flows in one direction, such as in a battery-powered circuit.
4. Voltage
Voltage, also known as electric potential difference, is the driving force that pushes electric charge through a conductor. It is measured in volts (V) and represents the difference in electric potential energy between two points. Higher voltage means more energy is available to move the charge.
Example: A battery has a voltage that pushes electrons through a circuit. A 9-volt battery has more "push" than a 1.5-volt battery, meaning it can provide more energy to move the charge through the circuit.
5. Resistance
Resistance is the opposition to the flow of electric current in a conductor. It is measured in ohms (Ω) and depends on the material, length, and cross-sectional area of the conductor. Higher resistance means more opposition to the flow of current.
Example: A long, thin wire has more resistance than a short, thick wire because the electrons have to travel a longer distance and through a smaller area, encountering more obstacles.
6. Ohm's Law
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them. Mathematically, it is expressed as \( I = \frac{V}{R} \), where \( I \) is the current, \( V \) is the voltage, and \( R \) is the resistance.
Example: If you have a circuit with a 12-volt battery and a 4-ohm resistor, the current through the circuit will be \( I = \frac{12V}{4Ω} = 3A \). This means 3 amperes of current will flow through the circuit.