Revision Notes: Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects

Class 8 Science Chapter 4: Electricity: Magnetic and Heating Effects — Quick Revision Notes

• Magnetic effect of current: discovered by Hans Christian Oersted (1820) — a current-carrying wire produces a magnetic field around it, deflecting a nearby compass needle.
• Electromagnet: a coil of wire that behaves like a magnet only while current flows through it; has North and South poles like a bar magnet, but is temporary and its poles reverse if the current direction is reversed.
• Electromagnet strength increases with more current (more cells), more coil turns, and adding an iron core.
• Heating effect of current: current flowing through a conductor’s resistance converts some electrical energy into heat.
• Nichrome has higher resistance than copper (for the same size), so it heats up more for the same current — used as the heating element in irons, heaters, kettles and toasters.
• Voltaic (chemical) cell: generates current via a chemical reaction between two different metal electrodes and an electrolyte (e.g., lemon juice, salt solution).
• Dry cells are single-use/disposable; rechargeable batteries can be recharged and reused many times.
• Every current-carrying conductor shows both the magnetic effect and the heating effect simultaneously, regardless of the conducting material.
• Everyday applications: magnetic effect — electric bells, cranes, motors, speakers; heating effect — irons, heaters, toasters, kettles.

Written by Satish

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