Electricity: Magnetic and Heating Effects — Class 8 MCQs with Answers

Electricity: Magnetic and Heating Effects — important questions & MCQs with answers (Class 8 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   The flow of electric charge through a wire is called:

   AgravityBelectric currentCsoundDonly heat
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   Answer: electric current

   Explanation: Electric current is defined as the flow of electric charge through a conductor; it is not defined by a single effect like heat, nor by unrelated phenomena such as gravity or sound.

2. Q2 of 6Easy

   When current flows through a wire, a nearby compass needle:

   AmeltsBdisappearsCgets heavierDdeflects (moves)
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   Answer: deflects (moves)

   Explanation: A current-carrying wire creates a magnetic field around it, which deflects a nearby compass needle — the magnetic effect of current, first seen by Oersted.

3. Q3 of 6Medium

   The strength of an electromagnet depends on:

   Athe colour of the wireBthe current and the number of turns of the coilCthe day of the weekDthe length of the switch
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   Answer: the current and the number of turns of the coil

   Explanation: An electromagnet's strength grows with both the current flowing through the coil and its number of turns — not with unrelated things like colour or the day.

4. Q4 of 6Medium

   A wire heats up when current flows because the current faces:

   Ano oppositionBa magnetCa switchDresistance (opposition to flow)
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   Answer: resistance (opposition to flow)

   Explanation: A wire heats up because its material offers resistance, opposing the flow of current, and that opposition converts some electrical energy into heat.

5. Q5 of 6Hard

   A compass near a wire deflects only when the switch is ON. This shows the current produces a:

   Aheat fieldBsound waveCmagnetic fieldDonly light
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   Answer: magnetic field

   Explanation: The needle deflects only while the switch is ON, showing the magnetic field exists solely because current is flowing — direct evidence of the magnetic effect of current.

6. Q6 of 6Hard

   Two electromagnets carry the same current, but one has more coil turns. The one with more turns will:

   Abe weakerBnot workConly get hotterDbe stronger and lift more clips
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   Answer: be stronger and lift more clips

   Explanation: More coil turns concentrate a stronger magnetic field for the same current, so the electromagnet with more turns is stronger and lifts more clips.

Electricity: Magnetic and Heating Effects notes: key concepts (Class 8 Science)

This chapter shows that an electric current does more than light a bulb — it has a magnetic effect and a heating effect. A current-carrying wire deflects a compass needle, which is how Oersted discovered that current creates a magnetic field. Winding the wire into a coil (with a soft iron core) makes an electromagnet whose strength grows with more turns and more current. Current also heats a conductor because of its resistance — the heating effect — which runs heaters, irons and bulbs, while the magnetic effect runs bells and motors.

Electric current and circuit

Electric current is the flow of charge around a closed circuit made of a cell, connecting wires, a switch and a component such as a bulb or LED.

Conductor and insulator

A conductor (like copper) lets current flow easily; an insulator (like plastic) does not, so it is used to cover wires safely.

Magnetic effect of current

A current-carrying wire deflects a nearby compass needle, showing that the current produces a magnetic field around itself — discovered by Hans Christian Oersted.

Magnetic field

The region around a current-carrying wire where the magnetic effect can be felt, for example by the deflection of a compass needle.

Electromagnet

A coil of wire, usually wound on a soft iron core, that becomes a magnet only while current flows and loses its magnetism when switched off.

Strength of an electromagnet

It increases with the number of turns of the coil, with the amount of current, and by using a soft iron core — a stronger electromagnet lifts more clips.

Heating effect of current

When current flows through a conductor it meets resistance, converting electrical energy into heat, so the conductor gets warm.

Resistance

The opposition a conductor offers to current; nichrome has a higher resistance than copper of the same size, so it heats up strongly while copper stays cool.

What the heat depends on

The heat produced in a wire depends on the current, the material, the thickness and length of the wire, and the time the current flows.

Everyday applications

The magnetic effect runs electric bells, motors, generators and crane electromagnets; the heating effect runs heaters, irons, toasters and glowing bulb filaments.