Electrical Energy — Important Questions

Conductors

Conductors are materials that allow electric current to flow through them easily because they have free electrons that can move freely. Metals like copper, aluminum, and silver are excellent conductors. These materials have low electrical resistance. Insulators like rubber, glass, and plastic resist the flow of current. Semiconductors have properties between conductors and insulators. Resistors are components that provide specific resistance in circuits. Good conductors are used in electrical wires, while insulators are used for safety and protection in electrical systems.

Electric iron

The heating effect of electric current (Joule's heating) occurs when electrical energy is converted to heat energy due to resistance in conductors. Electric iron uses this principle - current flows through a heating element with high resistance, generating heat for ironing clothes. The heat produced follows H = I²Rt formula. Electric fan uses magnetic effect for rotation, electric bell uses electromagnetic effect for sound, and electric motor uses magnetic effect for mechanical motion. Other heating appliances include electric heater, toaster, kettle, and room heaters.

Sum of all individual resistances

In a series circuit, resistors are connected end-to-end, forming a single path for current flow. The same current flows through all resistors. The equivalent resistance Rs = R₁ + R₂ + R₃. This happens because each resistor adds to the total opposition to current flow. The total voltage across the combination equals the sum of individual voltages (V = V₁ + V₂ + V₃). This makes the total resistance higher than any individual resistance. Series circuits are used in applications where we want the same current through all components, like decorative lights.

Kilowatt hour (kWh)

The commercial unit of electrical energy is kilowatt hour (kWh), also called 'unit' of electricity. It represents the energy consumed when 1 kilowatt power is used for 1 hour. 1 kWh = 1000 W × 3600 s = 3.6 × 10⁶ J. Electricity boards use this unit for billing because joule is too small for practical energy measurements. Watt is the unit of power, not energy. Ampere hour is used for battery capacity. Your electricity bill shows consumption in kWh units, and you pay per unit consumed.