Electricity: Magnetic and Heating Effects

About this chapter

Electricity: Magnetic and Heating Effects is Chapter 4 of Class 8 Curiosity. Through Sumana's lifting electromagnet, students meet three big ideas. First, the magnetic effect of current — a current-carrying wire deflects a nearby compass (Oersted, 1820); a coil with an iron core becomes an electromagnet whose strength depends on the number of cells, the number of turns and the direction of current; cranes' lifting electromagnets use this. Second, the heating effect — current through a conductor like nichrome produces heat because of resistance; heaters, kettles, irons, immersion rods and hair dryers all contain a heating element. Third, how a battery generates electricity — a Voltaic (Galvanic) cell uses two different electrodes in an electrolyte; a dry cell has a zinc container (negative) and a carbon rod with a metal cap (positive); rechargeable Li-ion batteries can be reused but slowly wear out. CTET Paper 2 tests electromagnet-strength reasoning, magnetic-vs-heating classification, why nichrome is chosen, electrode identification, lemon-cell circuits and dead-cell/rechargeable distinctions. The four tests — Practice 15, Quiz 15, Hard 15, Mastery 30 — cover these at exam depth.