Electricity

11.1 ELECTRIC CURRENT AND CIRCUIT

Electricity plays a vital role in modern society as a controllable and convenient form of energy used in homes, schools, hospitals, and industries. At its core, electricity involves the flow of electric charges through a conductor. When electric charge flows through a conductor such as a metallic wire, this flow is termed electric current. For example, in a torch, the cells or battery provide the flow of charges through the bulb, causing it to glow. The torch glows only when the switch is on because the switch completes the conducting path, forming a closed circuit. A continuous and closed path through which electric current flows is called an electric circuit. If the circuit is broken anywhere (for example, if the switch is off), the current stops flowing and the bulb does not glow. Electric current is quantitatively expressed as the amount of charge flowing through a particular cross-section of a conductor per unit time. Mathematically, if a net charge Q flows across any cross-section of a conductor in time t, then the current I is given by I = Q / t. The SI unit of electric charge is coulomb (C), where one coulomb corresponds to approximately 6 × 10^18 electrons. Since an electron carries a charge of 1.6 × 10^-19 C (negative), the conventional direction of current is taken opposite to the actual flow of electrons, which are negatively charged. This convention was established before the discovery of electrons. The unit of electric current is ampere (A), named after the French scientist Andre-Marie Ampere. One ampere corresponds to one coulomb of charge flowing per second. Smaller currents are expressed in milliampere (mA = 10^-3 A) or microampere (μA = 10^-6 A). An instrument called an ammeter is used to measure electric current and is always connected in series in the circuit so that the same current flows through it. The direction of current in a circuit is from the positive terminal of the cell to the negative terminal through the external circuit components. This section introduces the fundamental concept of electric current and electric circuit, setting the stage for understanding how electric charges move and how circuits are constructed and analyzed.

• Electric current is the flow of electric charges through a conductor.
• An electric circuit is a continuous and closed path for current flow.
• Current (I) is defined as charge (Q) flowing per unit time (t): I = Q / t.
• The SI unit of current is ampere (A), where 1 A = 1 C/s.
• Electrons flow from negative to positive terminal, but conventional current direction is opposite.
• An ammeter measures current and is connected in series in a circuit.
• 📌 Electric current: Rate of flow of electric charge through a conductor.
• 📌 Electric circuit: A closed path through which electric current flows.
• 📌 Ampere (A): SI unit of electric current, equal to one coulomb per second.

11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE

Electric charges flow in a conductor only when there is a difference in electric potential between two points, analogous to water flowing due to pressure difference. Just as water does not flow in a horizontal pipe without pressure difference, electric charges do not flow in a conductor without a potential difference. The potential difference (V) between two points in an electric circuit is defined as the work done (W) to move a unit charge (Q) from one point to another. Mathematically, V = W / Q. The SI unit of potential difference is volt (V), named after Alessandro Volta. One volt corresponds to one joule of work done in moving one coulomb of charge. A battery or cell maintains a potential difference across its terminals through chemical reactions, even when no current flows. When connected to a circuit, this potential difference drives the flow of charges, producing an electric current. The cell expends its chemical energy to maintain this current. The potential difference is measured using a voltmeter, which is always connected in parallel across the two points where the potential difference is to be measured. This section establishes the fundamental concept of electric potential difference as the driving force for current flow and introduces the volt as the unit of electric potential difference. **Table on page 4 (4×2)** | QUESTIONS | | | --- | --- | | 1. | Name a device that helps to maintain a potential difference across a conductor. | | 2. | What is meant by saying that the potential difference between two points is 1 V? | | 3. | How much energy is given to each coulomb of charge passing through a 6 V battery? |

• Electric charges flow only if there is a potential difference between two points.
• Potential difference (V) = Work done (W) / Charge (Q).
• SI unit of potential difference is volt (V), where 1 V = 1 J / 1 C.
• A battery maintains potential difference via chemical reactions.
• Voltmeter measures potential difference and is connected in parallel.
• Potential difference drives the flow of electric current.
• 📌 Electric potential difference: Work done per unit charge to move charge between two points.
• 📌 Volt (V): SI unit of electric potential difference.
• 📌 Voltmeter: Instrument used to measure potential difference, connected in parallel.