NCERT Solutions for Class 8th Science Chapter 4 Electricity: Magnetic and Heating Effects
Updated on 2026-09-19
About this chapter
When an electric current flows through a conductor such as a wire, it produces a magnetic field around it. This is the magnetic effect of electric current , and it is why a compass needle placed under a current carrying wire is deflected. Stop the current and the field disappears at once. A current carrying coil that behaves as a magnet is called an electromagnet . Every turn of the coil makes its own magnetic field, and because all the turns are wound the same way these fields point the same way inside the coil and add up — so a coil of 50 turns is far stronger than a single straight wire. An electromagnet has a North and a South pole , just like a bar magnet. Its strength is increased by increasing the current (more cells) or the number of turns , and its poles are reversed by reversing
- Chapter opener
- Does an Electric Current Have a Magnetic Effect?
- Electromagnets
- The Earth as a magnet
- and 4.2
- Does a Current Carrying Wire Get Hot?
- How Does a Battery Generate Electricity?
- Voltaic cell
- End-of-chapter questions
- Science, Society and Interdisciplinary Projects
Quick revision
| Term | What it means | Where it comes in the chapter | Everyday example |
|---|---|---|---|
| Magnetic field | The region around a magnet or a current carrying wire in which its magnetic effect can be felt | Section 4.1, page 48 | A compass needle turning when it is brought near a magnet |
| Magnetic effect of electric current | The production of a magnetic field around a conductor when current flows through it | Section 4.1, page 48 | The needle of a compass under a wire kicking the moment the switch is closed |
| Electromagnet | A current carrying coil that behaves as a magnet | Section 4.1.1, page 50 | The coil in an electric bell, a fan, a loudspeaker |
| Core | The iron rod or nail placed inside the coil to make the electromagnet stronger | Section 4.1.1, page 50 | The iron nail inside the coil in Activity 4.3 |
| Poles of an electromagnet | The two ends, North and South, whose polarity reverses if the current is reversed | Activity 4.4, pages 50–51 | End A and end B of the coil in Fig. 4.4 |
| Lifting electromagnet | A strong electromagnet hung from a crane, switched ON to lift and OFF to release | Section 4.1.2, page 52 | Sorting scrap iron in a scrap yard or a steel plant |
| Resistance | The opposition a conductor offers to the flow of electric current | Section 4.2, page 53 | Nichrome offers more resistance than copper of the same size and length |
| Heating effect of electric current | The generation of heat in a conductor because current is flowing through it | Section 4.2, page 53 | The filament of an incandescent lamp; a warm charger pin |
| Heating element | The rod or coil of wire in an appliance that is meant to become hot | Page 53 | The red-hot coil of an electric room heater or an electric stove |
| Electrode | One of the two metal rods, of different materials, dipped in the electrolyte of a cell | Section 4.3.1, page 55 | The copper wire and the iron nail in the lemon cell |
| Electrolyte | The liquid or paste — usually a weak acid or a salt solution — in which the electrodes are dipped | Section 4.3.1, page 55 | Lemon juice; salt solution; the moist paste inside a dry cell |
| Dead cell | A cell whose chemicals are used up, so it can supply no more electricity | Page 55 | A torch cell that no longer lights the lamp |
| Dry cell | A single use cell whose electrolyte is a thick moist paste, not a liquid | Section 4.3.2, page 57 | The cell in a wall clock or a TV remote |
| Rechargeable battery | A battery that can be charged and reused many times | Section 4.3.3, page 57 | Mobile phone, laptop, camera, inverter and electric vehicle batteries |
Exercises
- Chapter opener — Probe and ponder Page 46
- Activity 4.1: Let us investigate — Does an Electric Current Have a Magnetic Effect? Page 47–48
- In-text Questions — Electromagnets Page 49
- Activity 4.2: Let us explore — Electromagnets Page 49
- Activity 4.3: Let us experiment — Electromagnets Page 49–50
- In-text Questions — Electromagnets Page 50
- Activity 4.4: Let us investigate — Electromagnets Page 50–51
- Think like a scientist — Electromagnets Page 51
- The Earth as a magnet — A step further Page 51
- In-text Questions — and 4.2 Page 52
- Activity 4.5: Let us observe — Does a Current Carrying Wire Get Hot? Page 52–53
- Think like a scientist — Does a Current Carrying Wire Get Hot? Page 53
- In-text Questions — How Does a Battery Generate Electricity? Page 55 & 56
- Activity 4.6: Let us construct — Voltaic cell Page 56
- End-of-chapter questions — Keep the curiosity alive Page 58–61
- Science, Society and Interdisciplinary Projects — Discover, design, and debate Page 61