Extra Questions: Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects

Practice questions beyond the textbook exercise, testing deeper understanding of the magnetic and heating effects of electric current for Class 8 Science Chapter 4. These Class 8 Science Chapter 4 important questions are handy for last-minute exam practice.

Last Updated: September 23, 2026

Extra Questions: Class 8 Science Chapter 4 Electricity Magnetic and Heating Effects

1. 1 (Assertion-Reason). Assertion: Reversing the current in an electromagnet reverses its poles. Reason: The direction of a magnetic field around a conductor depends on the direction of current flow.
   Solution: Both true, and the reason correctly explains the assertion.
2. 2 (Short Answer). Name the scientist who first discovered that electric current produces a magnetic effect.
   Solution: Hans Christian Oersted.
3. 3 (Applied). Two electromagnets are identical except one has 50 turns and the other has 100 turns of wire, carrying the same current. Which lifts more paper clips, and why?
   Solution: The 100-turn electromagnet — more turns produce a stronger magnetic field for the same current.
4. 4 (Assertion-Reason). Assertion: Nichrome is preferred over copper for heating elements. Reason: Nichrome has lower resistance than copper.
   Solution: Assertion is true, but the reason is false — nichrome actually has higher resistance than copper, which is why it heats up more.
5. 5 (Short Answer). What is an electrolyte?
   Solution: A solution (or paste) that conducts electricity by allowing ions to move, enabling the chemical reaction in a Voltaic cell.
6. 6 (Applied). Why does an electromagnet lose its magnetism as soon as the current is switched off, unlike a bar magnet?
   Solution: An electromagnet’s magnetism comes entirely from the current-generated magnetic field; once current stops, that field disappears. A bar magnet’s magnetism comes from permanently aligned internal magnetic domains, not from current.
7. 7 (Synthesis). A student wants to make a stronger electromagnet without adding more cells. Suggest one way.
   Solution: Increase the number of turns of wire in the coil (or insert/use a stronger iron core).
8. 8 (Assertion-Reason). Assertion: A wire carrying current always gets warm, however small the current. Reason: All conductors have some resistance, and current through resistance always generates heat.
   Solution: Both true, and the reason correctly explains the assertion (though the warming may be too small to notice with very small currents).
9. 9 (Short Answer). Give one everyday application each of the magnetic effect and the heating effect of current.
   Solution: Magnetic effect: electric bell/doorbell or electromagnetic crane. Heating effect: electric iron or room heater.
10. 10 (Applied). Why does a lemon cell with only one lemon often fail to light an LED, but two or three lemons connected in series succeed?
    Solution: A single lemon cell produces only a small voltage; connecting several in series adds their voltages together, eventually reaching the minimum voltage the LED needs to glow.

Frequently Asked Questions

Why do some materials get hot when a large current passes through them, while good conductors stay relatively cool?
Materials with higher electrical resistance oppose the flow of current more strongly, converting more electrical energy into heat, which is why resistive materials like a bulb filament heat up compared to good conductors.

How can the magnetic effect of current be demonstrated using a simple compass needle?
When a compass needle is placed near a wire carrying an electric current, the needle deflects from its usual position, showing that the flowing current has created a magnetic field around the wire.

Written by Satish

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