How can poles of an electromagnet be reversed?

By changing direction of current

What makes rechargeable batteries wear out?

Repeated charge-discharge cycles

NCERT Solutions Class 8 Science - Curiosity Chapter 4 – Electricity: Magnetic and Heating Effects

Name: Electricity: Magnetic and Heating Effects – Class 8 Science - Curiosity
Uploaded: 2026-05-31
Description: Electric current creates both magnetic and heating effects. It can make wires behave like magnets, forming electromagnets used in cranes and machines. Current also produces heat, which powers devices like irons and heaters, while batteries and cells provide the energy that drives these effects.

Class 8 Science - Curiosity

Last Updated: 31 May 2026

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Chapter Introduction

Electric current creates both magnetic and heating effects. It can make wires behave like magnets, forming electromagnets used in cranes and machines. Current also produces heat, which powers devices like irons and heaters, while batteries and cells provide the energy that drives these effects.

हिंदी में (Hindi)

विद्युत धारा से चुंबकीय और ऊष्मीय प्रभाव उत्पन्न होते हैं। यह तारों को चुंबक की तरह व्यवहार करने में सक्षम बनाती है, जिससे विद्युतचुंबक बनते हैं। यही धारा तारों को गर्म करती है और इस्त्री, हीटर जैसे उपकरण चलाती है, जबकि बैटरी और सेल इन्हें ऊर्जा प्रदान करते हैं।

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Important Points

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Practice MCQ Questions (60 questions)

Q1. What did Mohini and Aakarsh see at the science exhibition?

Q2. What material was used as a core in the electromagnet model?

Q3. Who discovered that electricity and magnetism are linked?

Q4. When does a current-carrying wire produce a magnetic field?

Q5. What happens to a compass needle when current flows through a nearby wire?

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Frequently Asked Questions (FAQ)

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Tough Words (Glossary)

Exhibition

Meaning: Public display of items or projects

अर्थ: प्रदर्शनी

"The science exhibition was crowded and exciting."

Exhibit

Meaning: An item or model shown to the public

अर्थ: प्रदर्श

"Each exhibit showed a different science idea."

Electromagnet

Meaning: A magnet made by electric current through a coil

अर्थ: विद्युतचुंबक

"The electromagnet lifted paper clips when the switch was on."

Circuit

Meaning: A complete path for electric current

अर्थ: परिपथ/सर्किट

"Close the circuit to let the current flow."

Compass

Meaning: Tool with a magnetic needle pointing north

अर्थ: दिशा सूचक/कंपास

"The compass needle moved when current flowed."

Deflection

Meaning: A change in direction or position

अर्थ: विचलन/झुकाव

"We noted the deflection of the needle near the wire."

Phenomenon

Meaning: An observable event or fact

अर्थ: प्रकटन/घटना

"The magnetic effect of current is a useful phenomenon."

Magnetic field

Meaning: Region where a magnet’s effect can be felt

अर्थ: चुंबकीय क्षेत्र

"A current-carrying wire creates a magnetic field."

Conductor

Meaning: Material that allows electric current to pass

अर्थ: चालक

"Copper is a good conductor of electricity."

Insulated (wire)

Meaning: Covered to stop current from leaking out

अर्थ: रोधित/इंसुलेटेड (तार)

"Use insulated wire to make the coil."

Coil

Meaning: Wire wound in loops or turns

अर्थ: कुंडली/कॉयल

"More turns in the coil make a stronger magnet."

Core

Meaning: Material placed inside a coil to strengthen it

अर्थ: केंद्र/कोर

"An iron core increases the strength of an electromagnet."

Polarity

Meaning: Property of having north and south poles

अर्थ: ध्रुवता

"We checked the polarity of the electromagnet’s ends."

Terminal

Meaning: End point of a battery or device for connections

अर्थ: टर्मिनल/छोर

"Connect the wire to the positive terminal."

Suspended (freely)

Meaning: Hanging and free to align itself

अर्थ: स्वतंत्र रूप से लटका

"A freely suspended magnet points north–south."

Migratory

Meaning: Moving from one region to another seasonally

अर्थ: प्रवासी

"Migratory birds navigate using Earth’s field."

Navigate

Meaning: Find the way to a place

अर्थ: मार्ग ढूँढना/नेविगेट करना

"Sea turtles navigate long distances."

Shield

Meaning: Protect from harm by blocking

अर्थ: ढाल बनना/सुरक्षा देना

"Earth’s field shields us from harmful particles."

Crane

Meaning: Machine used to lift heavy objects

अर्थ: क्रेन

"A crane used a lifting electromagnet in the yard."

Scrap yard

Meaning: Place where waste metal is collected

अर्थ: कबाड़खाना/स्क्रैप यार्ड

"Electromagnets sort metal in a scrap yard."

Nichrome

Meaning: An alloy wire with high resistance

अर्थ: नाइक्रोम

"Nichrome wire becomes hot when current flows."

Resistance

Meaning: Opposition to the flow of electric current

अर्थ: प्रतिरोध

"Higher resistance produces more heat."

Heating effect

Meaning: Warming caused when current flows in a conductor

अर्थ: धारा का ऊष्मीय प्रभाव

"The heating effect makes a filament glow."

Filament

Meaning: Thin wire that glows in a bulb

अर्थ: फिलामेंट

"An incandescent bulb has a tungsten filament."

Appliance

Meaning: Electrical device used at home or work

अर्थ: उपकरण/उपकरण

"Heaters and kettles are heating appliances."

Immersion rod

Meaning: Electric heater put directly in water

अर्थ: इमर्शन रॉड/डुबकी रॉड

"Use an immersion rod to heat water."

Furnace

Meaning: Enclosed structure for high temperatures

अर्थ: भट्टी

"A furnace melts scrap steel for recycling."

Transmission

Meaning: Carrying electricity over wires to distances

अर्थ: संचरण/प्रेषण

"Energy is lost as heat during transmission."

Voltaic cell (Galvanic cell)

Meaning: Cell that generates electricity from chemical reactions

अर्थ: वोल्टाइक कोश/गैल्वैनिक कोश

"A lemon can act like a simple voltaic cell."

Electrode

Meaning: Metal plate/rod in a cell where reactions occur

अर्थ: विद्युद्रोध/इलेक्ट्रोड

"Copper and zinc were used as electrodes."

Electrolyte

Meaning: Liquid/paste that conducts inside a cell

अर्थ: विद्युत अपघट्य

"Lemon juice is the electrolyte in the lemon cell."

LED

Meaning: Light Emitting Diode; a tiny light device

अर्थ: एलईडी (प्रकाश उत्सर्जक डायोड)

"Several lemons in series can light an LED."

Rechargeable

Meaning: Able to be recharged and used again

अर्थ: पुनर्भरणीय/रिचार्ज होने योग्य

"Rechargeable batteries reduce waste."

Lithium‑ion

Meaning: Common modern rechargeable battery type

अर्थ: लिथियम‑आयन

"Phones mostly use lithium‑ion batteries."

Cobalt

Meaning: Metal used in some batteries

अर्थ: कोबाल्ट

"Cobalt is mined for battery materials."

Solid‑state (battery)

Meaning: Battery using solid electrolyte

अर्थ: ठोस‑अवस्था (बैटरी)

"Solid‑state batteries may charge faster."

Paste (electrolyte)

Meaning: Thick moist mixture used in dry cells

अर्थ: लेप/पेस्ट (विद्युत अपघट्य)

"A dry cell uses a paste electrolyte."

Container

Meaning: Holder or case for something

अर्थ: पात्र/डिब्बा

"The electrolyte is kept in a container."

Zinc

Meaning: Metal that often acts as negative terminal

अर्थ: जस्ता

"A dry cell has a zinc container."

Carbon rod

Meaning: Central positive terminal in a dry cell

अर्थ: कार्बन दंड

"The carbon rod is the positive terminal."

Adhesive tape

Meaning: Sticky strip used to hold things together

अर्थ: चिपकने वाली टेप

"Fix the coil with adhesive tape."

Cylindrical

Meaning: Shaped like a cylinder

अर्थ: बेलनाकार

"Wind 50 turns on the cylindrical form."

Gauge (wire)

Meaning: Standard thickness of a wire

अर्थ: गेज/तार मोटाई

"Use 26–28 gauge nichrome wire."

Magnitude (of current)

Meaning: Size or amount of something

अर्थ: परिमाण (धारा का)

"More magnitude of current makes stronger magnets."

Investigate

Meaning: To carry out a careful study or test

अर्थ: जाँच/अनुसंधान करना

"We will investigate how turns affect strength."

Observe

Meaning: To watch carefully and note details

अर्थ: अवलोकन करना

"Observe the compass while switching on and off."

Generator

Meaning: Machine that produces electricity

अर्थ: जनित्र/जनरेटर

"Power stations use generators to make electricity."

Incandescent

Meaning: Glowing because of heat

अर्थ: तापदीप्त

"An incandescent lamp gets warm when lit."

Battery

Meaning: One or more cells that supply electricity

अर्थ: बैटरी

"A battery of two cells gave a stronger field."

Switch

Meaning: Device to open or close a circuit

अर्थ: स्विच

"Turn the switch off to drop the clips."

NCERT Solutions Class 8 Science - Curiosity Chapter 4 – Electricity: Magnetic and Heating Effects

Chapter Introduction

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Important Points

Practice MCQ Questions (60 questions)

Q1. What did Mohini and Aakarsh see at the science exhibition?

Q2. What material was used as a core in the electromagnet model?

Q3. Who discovered that electricity and magnetism are linked?

Q4. When does a current-carrying wire produce a magnetic field?

Q5. What happens to a compass needle when current flows through a nearby wire?

Q6. What is the region around a current-carrying wire where magnetic effect can be felt called?

Q7. What disappears when current stops flowing through a wire?

Q8. Which scientist was the first to observe deflection of compass due to current?

Q9. What is the function of an electromagnet?

Q10. Which metal is used in an electromagnet core?

Q11. What happens when an electromagnet’s circuit is opened?

Q12. How can an electromagnet be made stronger?

Q13. What determines the poles of an electromagnet?

Q14. If north pole of compass is attracted to end A of an electromagnet, end A is a:

Q15. How can poles of an electromagnet be reversed?

Q16. Which natural object behaves like a giant magnet?

Q17. What creates Earth’s magnetic field?

Q18. Migratory birds use Earth’s ______ to navigate.

Q19. Where are lifting electromagnets used?

Q20. How does a lifting electromagnet work?

Q21. What happens to magnetic field when current is switched OFF?

Q22. Who invented the Voltaic cell?

Q23. What are the plates in a Voltaic cell called?

Q24. What is the function of electrolyte in a cell?

Q25. What does a Voltaic cell produce?

Q26. When a cell stops working, it is called:

Q27. Who observed that a frog’s leg moved when touched with metals?

Q28. Which metals did Galvani use in his experiment?

Q29. Volta used _______ instead of frog’s leg to create electric current.

Q30. What experiment can create electricity using lemons?

Q31. In a lemon cell, what are the electrodes?

Q32. What acts as the electrolyte in a lemon cell?

Q33. If LED doesn’t glow in lemon cell, what should be done?

Q34. Which metals form a common pair for Voltaic cells?

Q35. Which part of dry cell acts as negative terminal?

Q36. In a dry cell, which part acts as positive terminal?

Q37. Why is it called a dry cell?

Q38. What type of batteries can be reused?

Q39. Which is the most common rechargeable battery today?

Q40. What makes rechargeable batteries wear out?

Q41. What are lithium and cobalt used for?

Q42. Which future battery uses solid electrolytes?

Q43. What happens to a wire when electric current flows through it?

Q44. Which wire is used in heating effect experiment?

Q45. What causes the heating of a wire?

Q46. The heating effect of current converts electrical energy into ______.

Q47. Nichrome wire offers ______ resistance than copper wire.

Q48. Which household device works on heating effect of current?

Q49. What is the wire in heating devices called?

Q50. Which of the following is a safety measure in circuits?

Q51. Which phenomenon helps melt steel in furnaces?

Q52. Which scientist discovered the first battery?

Q53. Which unit is used for electric current?

Q54. What causes a stronger electromagnet?

Q55. What is the paste in dry cell called?

Q56. Which type of energy conversion happens in a Voltaic cell?

Q57. Which material in Earth’s core helps generate magnetic field?

Q58. Who discovered that an electric current produces a magnetic field?

Q59. What is the heating effect of electric current used for?

Q60. What makes electric irons and stoves work?