Class 8 Science · Original EZT practice
Electricity: Magnetic and Heating Effects (Class 8 Science Chapter 4): what current does besides lighting a bulb
Switch on a torch and the bulb glows - but that same electric current can also make things hot and behave like a magnet. This chapter explores those two hidden effects of current, and how they run your iron, your fuse and even junkyard cranes. Below: the ideas in plain words, then original EZT practice with worked answers. (Note: this is original practice, not a textbook exercise key.)
10 original worked examples, 10 fresh self-check questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 17 October 2026:
1. Electric current needs a closed path
Current flows only around a complete circuit: cell, wires, device and back to the cell. A switch opens or closes that path.
2. The heating effect of current
When current passes through a wire, part of the electrical energy becomes heat. Thin, high-resistance wires heat the most, which is why filaments glow and irons warm up.
3. Fuses: heating effect as a safety device
A fuse is a short piece of low-melting wire. If too much current flows, the fuse melts first and breaks the circuit before wiring or appliances are damaged.
4. The magnetic effect of current
A current-carrying wire behaves like a magnet and can deflect a compass needle. A coil concentrates the effect and forms an electromagnet that can be switched on and off.
5. Safe habits around electricity
Water and damp hands can carry current to your body. Never touch switches with wet hands, poke objects into sockets or handle a blown fuse without switching off the main supply.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Explain a broken circuit
Choose the method: Trace the path from the cell through the device and back; any gap stops current.
EZT practice question
A torch works only when its cap is screwed on fully. Why?
Show the worked solution
- A loose cap leaves a gap in the circuit.
- Tightening the cap closes the path for current.
Answer: The loose cap opens the circuit; tightening it completes the circuit.
Check: Current needs a closed loop through the cell, bulb and cap.
Watch for this: The bulb is not necessarily faulty when a gap stops the current.
Now try it yourself
A fairy-light string goes off when one joint is unplugged. Why?
Check your answer
The circuit is open.
Current cannot cross the gap at the unplugged joint.
Sort appliances by current effect
Choose the method: Ask whether the appliance mainly makes heat or uses a motor based on magnetic force.
EZT practice question
Sort these by the effect each mainly uses: electric iron, ceiling fan, electric kettle and washing machine.
Show the worked solution
- Iron and kettle are made to produce heat.
- Fan and washing machine use electric motors.
Answer: Heating effect: iron and kettle. Magnetic effect: ceiling fan and washing machine.
Check: A motor turns electrical energy into motion through magnetic effects.
Watch for this: A fan may warm slightly, but heating is not its main working effect.
Now try it yourself
Which effect mainly drives an electric bell?
Check your answer
The magnetic effect.
The bell uses an electromagnet to move its striker.
Explain why a filament is thin
Choose the method: Connect smaller conducting area with higher resistance and stronger heating.
EZT practice question
Why is a bulb filament made of thin wire rather than thick wire?
Show the worked solution
- A thin filament offers more resistance.
- More electrical energy becomes heat, so it glows.
Answer: The thin wire heats enough to give light.
Check: A thick low-resistance wire would not reach the same glowing temperature as easily.
Watch for this: Thin does not mean disconnected; the circuit still remains closed.
Now try it yourself
Why does a heater coil glow more than its thick supply cord?
Check your answer
The coil has higher resistance.
Higher resistance turns more electrical energy into heat.
Explain fuse-wire choice
Choose the method: A safety wire must fail before the protected wiring is harmed.
EZT practice question
Why must a fuse wire melt easily?
Show the worked solution
- Excess current heats the fuse wire.
- It melts at a lower current than the protected circuit can safely carry.
Answer: So it breaks the circuit before the dangerous current damages anything else.
Check: The fuse is deliberately the weakest safe link.
Watch for this: A high-melting wire would keep conducting when the fuse should have blown.
Now try it yourself
What should a good fuse do during an overload?
Check your answer
Melt and open the circuit.
Opening the circuit stops the excess current.
Respond to a repeatedly blowing fuse
Choose the method: Treat the fuse as a warning sign, not as a part to bypass.
EZT practice question
A fuse blows the moment a faulty heater is switched on. What does that tell you, and what should you do?
Show the worked solution
- The heater is drawing too much current.
- The fuse is cutting off the circuit for safety.
Answer: Leave the heater off and have it repaired; never replace the fuse with plain thick wire.
Check: Bypassing the fuse removes the safety cut-off.
Watch for this: Do not keep replacing fuses without finding the fault.
Now try it yourself
Why is a copper wire unsafe as a fuse replacement?
Check your answer
It may not melt on overload.
The excess current can then overheat the wiring.
Recognise the magnetic effect
Choose the method: Look for a compass needle moving near a current-carrying wire.
EZT practice question
A compass placed under a straight current-carrying wire moves. What does that show?
Show the worked solution
- The compass responds to magnetism.
- The current in the wire creates a magnetic effect around it.
Answer: Electric current produces magnetism around the wire.
Check: The deflection disappears when the current is switched off.
Watch for this: The compass is not being pushed by the wire physically.
Now try it yourself
What simple tool can show the magnetic effect of current?
Check your answer
A compass needle.
It deflects near a current-carrying wire.
Compare electromagnets and permanent magnets
Choose the method: Think about control: switching, strength and shape.
EZT practice question
Give two advantages of an electromagnet over a permanent magnet.
Show the worked solution
- An electromagnet works only while current flows.
- Changing current or coil turns changes its strength.
Answer: It can be switched on and off, and its strength can be adjusted.
Check: A permanent magnet cannot be switched off in this way.
Watch for this: An electromagnet is not stronger in every design; control is the key advantage.
Now try it yourself
Name one use of an electromagnet.
Check your answer
A junkyard crane or electric bell.
Both need magnetism that can be controlled.
Explain a switching electromagnet
Choose the method: Connect current on with attraction and current off with release.
EZT practice question
A junkyard crane lifts a car and drops it at another spot without hooks. How?
Show the worked solution
- Current makes the crane magnet attract the car.
- Switching the current off removes the attraction.
Answer: The crane uses an electromagnet that switches on to lift and off to release.
Check: No hook is needed because magnetic force holds the iron car body.
Watch for this: The car is not glued; it drops when the current stops.
Now try it yourself
What happens to scrap iron held by the crane when power fails?
Check your answer
It can fall.
The electromagnet loses its magnetism without current.
Explain the wet-hand shock risk
Choose the method: Treat water on the skin as a possible conducting path.
EZT practice question
Why is it dangerous to touch a switch with wet hands?
Show the worked solution
- Water can conduct electric current.
- The current may pass from the switch to your body.
Answer: Wet hands increase the risk of electric shock.
Check: Dry hands and insulated surfaces reduce the chance of a conducting path.
Watch for this: Do not assume a plastic-looking switch is safe to touch when wet.
Now try it yourself
What should you do before touching a switch after washing your hands?
Check your answer
Dry your hands fully.
This removes the water path that can conduct current.
Distinguish motor action from heating
Choose the method: Ask what energy change the appliance is designed to produce.
EZT practice question
Why does a fan not work mainly on the heating effect of current?
Show the worked solution
- A fan is designed to move its blades.
- Its motor uses magnetic effects to produce rotation.
Answer: The fan mainly uses the magnetic effect, not the heating effect.
Check: Some heat is produced as a side effect, but rotation is the useful output.
Watch for this: Do not classify every appliance with a wire as a heating appliance.
Now try it yourself
Which effect mainly makes a room heater warm?
Check your answer
The heating effect.
The heater is designed to convert electrical energy into heat.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Name two effects of electric current with one appliance for each.
- What does a fuse do when current gets too high?
- How would you show the magnetic effect of current with just a battery, wire and compass?
- Why does a fan not work on the heating effect?
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Questions about this practice page
- What is the heating effect of electric current?
- When current flows through a wire, some electrical energy becomes heat - the principle behind bulb filaments, irons, kettles and fuses.
- What is the magnetic effect of electric current?
- A current-carrying wire acts like a magnet and can deflect a compass needle; a coil can form a strong electromagnet.
- How does a fuse protect a circuit?
- Its low-melting wire heats and melts when current exceeds a safe level, breaking the circuit before appliances or wiring are damaged.
- What is an electromagnet?
- A coil of wire, often around an iron core, that becomes a magnet only while current flows. It is switchable and adjustable.
- Are these the NCERT exercise questions for Electricity: Magnetic and Heating Effects?
- No. EZT pages are original practice on this chapter - use them to prepare for the textbook exercises, not as a substitute for your book.