Electricity class 10 Full chapter in animation | NCERT Science chapter 12

Understanding Electric Circuits and Current Electricity is a vital energy source, powering homes, schools, hospitals, and industries. An electric circuit consists of components like cells, wires, switches, and bulbs; it allows the flow of electric current when complete. The direction of this current can be described as conventional (positive to negative) or electron flow (negative to positive). Electric current measures charge movement over time using the formula I = Q/T with units in amperes (A), while smaller currents use milliamperes or microamperes.

Exploring Potential Difference and Circuit Diagrams Potential difference drives electricity between two points due to varying potential energies—similar to water flowing from one tank at higher potential energy into another at lower potential. Voltage quantifies this difference in volts (V), measured by an instrument called a voltmeter connected parallelly across points. Circuit diagrams simplify understanding through standard symbols for elements like batteries or resistors; these visual representations aid comprehension of electrical systems' functionality.

In 1827, German physicist George Simon Ohm introduced a law explaining the relationship between voltage (V), current (I), and resistance (R) in an electric circuit. Voltage acts as the force driving charges through a circuit, while current is their flow; resistance opposes this flow. According to Ohm’s Law, current is directly proportional to voltage and inversely proportional to resistance: V = IR or I = V/R. To verify this experimentally, one can measure voltages and currents using cells connected in series with instruments like ammeters and voltmeters. By plotting these values on a graph of potential difference versus current for different cell configurations—1 cell yielding 0.15A at 0.3V up to four cells producing 0.5A at 1V—a straight line confirms that V/I remains constant across varying conditions; this constant represents R or Resistance measured in ohms ("). Additionally adjustable resistors called rheostats allow control over electrical circuits by modifying effective resistances without altering power sources.

Resistance arises in conductors due to the attraction between electrons and atoms, which slows down electron movement. This opposition to electric current varies across materials. An experiment demonstrates this: wire A allows high current flow (good conductor), wire B permits moderate flow (resistor), wire C restricts it significantly (poor conductor), while wire D blocks it entirely (insulator). Good conductors have low resistance, resistors allow some current with moderate resistance, poor conductors permit minimal flow due to higher resistance, and insulators prevent any significant electrical passage.

Factors Influencing Resistance and Resistivity Resistance in a conductor depends on its length, cross-sectional area, and material. Longer conductors have higher resistance; wider ones have lower resistance. The formula R = ρL/A relates these factors where resistivity (ρ) is unique to each material, indicating how much it opposes current flow. Metals like copper and aluminum are excellent conductors due to low resistivity while alloys with higher resistivities are used for their heat-resistant properties.

Resistors: Series vs Parallel Connections In series connections, all current flows through one path; total voltage equals the sum of individual voltages across each resistor while total resistance increases as more resistors are added (R_total = R1 + R2 + ...). In parallel connections, multiple paths allow divided currents based on individual resistor values; all share the same voltage but adding more reduces overall resistance following 1/R_total = 1/R1 + 1/R2 + ....

When electric current flows through a conductor, resistance converts part of the electrical energy into heat. This heating effect is evident in devices like fans that become hot after prolonged use. Materials with higher resistance are specifically used to generate significant heat, as seen in appliances like electric irons. Joule’s law explains this phenomenon by stating that the heat produced (H) is proportional to the square of the current (I²), resistance (R), and time duration (T). Higher currents or resistances result in greater collisions among electrons within conductors, increasing thermal energy output.

Electric heaters utilize Joule's law to convert electrical energy entirely into heat, effectively warming spaces. In electric irons, the generated heat is applied for pressing clothes efficiently. Electrical fuses are designed based on this principle; they melt and break circuits when excessive current flows, preventing potential damage by leveraging the heating effect described by Joule’s law.