How to see a current
A circuit, and no lamp.
One cell, a switch, a length of wire and nothing to light up. Can you still tell whether current flows?
📚 Chapter Learning Kit
Electricity: Magnetic and Heating Effects · Class 8 Science · Curiosity
English 5 topics 175 leveled MCQs 85 flashcards 5 games Free
Shared by a Veda teacher · Generated with Veda AI · Oct 2026
⚡ Veda Bites
💡 Concept
💡 Tip
💡 Concept
💡 Concept
💡 Tip
💡 Concept
The whole idea, one bite at a time
Veda Bites are swipeable micro-lessons — each one teaches exactly one idea. Here's a taste from this kit; the app has the full deck.
What the needle does
Aside, then back.
Close the switch and the needle swings away from north. Open it and the needle returns.
Why this is strange
Look for the magnet.
A compass needle has only ever moved near a magnet, and there is no magnet in this circuit.
The model at the exhibition
A hook that lets go.
An iron nail wrapped in wire, joined to a battery, picking up paper clips and dropping them again.
Why wind it into a coil
Turns add up.
A straight wire carrying a current has a field around it, but a weak one.
The coil alone
Even with nothing inside.
Put a compass at each end of an empty coil and connect a cell. Both needles deflect.
📖 Smart notes
What you'll study, topic by topic
1
The Magnetic Effect of a Current
A current flowing in a wire produces a magnetic field around it, and the field lasts exactly as long as the current does. A compass needle is how you see it - and Oersted saw it by accident in 1820.
- A current flowing through a conductor produces a magnetic field around it.
- This is called the magnetic effect of electric current.
- The field exists only while the current flows.
~45 min · full explanation, examples & memory tricks in the app
2
Electromagnets
Wind a current carrying wire into a coil and it becomes a magnet; put iron inside and it becomes a strong one. It has two poles, they reverse with the current, and the whole thing starts and stops with a switch.
- A coil with a current in it acts as a magnet, and that is what an electromagnet is.
- An empty coil already deflects a compass at each of its ends.
- An iron core makes the same coil and current far stronger.
~50 min · full explanation, examples & memory tricks in the app
3
The Heating Effect of a Current
A current warms every conductor it flows through, because the conductor resists it and resistance turns electrical energy into heat. That one effect boils a kettle and melts a plug.
- A current flowing through any conductor warms that conductor.
- The conductor opposes the flow, and that opposition is resistance.
- Resistance turns some of the electrical energy into heat.
~50 min · full explanation, examples & memory tricks in the app
4
Inside a Voltaic Cell
A cell holds chemicals, not electricity. Two different metals in a liquid that conducts, a reaction between them, and a current for as long as the chemicals last.
- A Voltaic cell is also called a Galvanic cell.
- It has two rods of different metals, called the electrodes.
- They stand partly in a liquid called the electrolyte.
~45 min · full explanation, examples & memory tricks in the app
5
Dry Cells and Rechargeable Batteries
Trading the liquid for a paste made a cell portable, but it is still used once. A rechargeable battery goes back on charge instead, saves waste and money, and wears out slowly rather than suddenly.
- A Voltaic cell holds a liquid in an open jar, so it cannot be carried about.
- A dry cell is called dry because its electrolyte is a thick moist paste.
- The zinc container is the negative terminal of the cell.
~45 min · full explanation, examples & memory tricks in the app
❓ Leveled MCQ practice
Try the smart MCQs from this kit
175 questions laddered from warm-up to topper-level, each with an explanation. A taste:
What exactly does the deflection of the compass needle show?
Intermediate
A The current has produced a magnetic field around the wire
B The wire has become a permanent magnet from that point on
C The compass needle has lost its own magnetism
D The cardboard between them has been magnetised
Show answer & explanation
The current has produced a magnetic field around the wire
The needle is a small magnet, and something magnetic has to be present to turn it. Here that something is the field of the current.
What is produced around a wire when a current flows through it?
Beginner
A A beam of bright light
B A sound wave
C A water drop
D A magnetic field
Show answer & explanation
A magnetic field
The region where that effect can be felt is the field.
A pupil closes a switch and the compass needle under the wire swings aside, then returns the moment he opens it again. What does that tell him?
Intermediate
A The compass needs a stronger cell
B The needle has been damaged a little by the swing
C The field lasts only while the current flows
D The wire is now a magnet for good
Show answer & explanation
The field lasts only while the current flows
Stop the current and the field goes with it, which is why the needle comes back to north.
Read these statements about the activity. I. The needle swings aside while the switch is closed. II. It returns to north when the switch is opened. III. A magnet had to be placed in the circuit for this. Which are correct?
Intermediate
A I and II only
B II and III only
C I and III only
D I, II and III
Show answer & explanation
I and II only
There is no magnet in the circuit at all. A cell, a switch and a wire are the whole of it.
🃏 Flashcards
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85 flashcards in this kit — the app reviews them with spaced repetition so the right card returns on the right day.
🎮 Learning games
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Categorization
Fact Or Myth
Sequence Builder
Memory Match
Speed Quiz
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