This chapter explains electricity as a vital and controllable form of energy used in daily life. It introduces electric current, electric circuits, potential difference, and resistance, and explains their relationships through Ohm’s law. The chapter further discusses series and parallel combinations of resistors, the heating effect of electric current, Joule’s law of heating, and electric power, helping students understand how electrical devices work safely and efficiently.
Key Points
Electric current is the flow of electric charges through a conductor.
A closed electric circuit is necessary for current to flow.
Electric current (I) is defined as the rate of flow of charge: I = Q/t.
The SI unit of current is ampere (A).
Potential difference (V) is the work done per unit charge: V = W/Q.
The SI unit of potential difference is volt (V).
Ammeter measures current and is connected in series.
Voltmeter measures potential difference and is connected in parallel.
Ohm’s Law states that V ∝ I, or V = IR, at constant temperature.
Resistance (R) opposes the flow of current; its unit is ohm (Ω).
Resistance depends on length, area of cross-section, and material.
Resistivity (ρ) is a material property and is independent of dimensions.
In series combination, total resistance increases: Rs = R₁ + R₂ + R₃.
In parallel combination, total resistance decreases: 1/Rp = 1/R₁ + 1/R₂ + 1/R₃.
Heating effect of electric current converts electrical energy into heat.
Joule’s law of heating: H = I²Rt.
Heating effect is used in electric irons, heaters, bulbs, and fuses.
Electric power (P) is the rate of consumption of electrical energy.
P = VI = I²R = V²/R.
The SI unit of power is watt (W).
Commercial unit of electrical energy is kilowatt-hour (kWh) or unit.
Parallel circuits are preferred in homes for safety and proper functioning.
👉 👉Understanding electricity helps us use electrical energy safely, efficiently, and economically. Knowledge of circuits, resistance, and power prevents accidents, reduces energy waste, and forms the foundation for modern technology and responsible energy usage.