Electricity: Magnetic & Heating Effects Class 8 (Curiosity)

Q 1
Question
(i) The solution used in a Voltaic cell is called ____. (ii) A current carrying coil behaves like a ____.
🔗 Concept:
4.3.1
Voltaic Cell
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(i) Electrolyte. (ii) Magnet (electromagnet).
Explanation
The liquid in a Voltaic cell is the electrolyte.
It is usually a weak acid or salt solution.
A coil with current acts like a magnet, called an electromagnet.
Electrolyte makes current; a current carrying coil acts as a magnet.

Q 2
Question
State True or False: (i) Dry cells are less portable than Voltaic cells. (ii) A coil becomes an electromagnet only when current flows. (iii) An electromagnet with a single cell attracts more clips than the same one with 2 cells.
🔗 Concept:
4.1.1
Electromagnets
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(i) False. (ii) True. (iii) False.
Explanation
(i) Dry cells are more portable than Voltaic cells, not less.
(ii) A coil acts as an electromagnet only while current flows.
(iii) Two cells give more current, so they attract more clips than one cell.
More current means a stronger electromagnet, not a weaker one.

Q 3
Question
An electric current flows through a nichrome wire for a short time. (i) The wire becomes warm. (ii) A magnetic compass placed below the wire is deflected. Choose the correct option:
(a) Only (i) is correct
(b) Only (ii) is correct
(c) Both (i) and (ii) are correct
(d) Both (i) and (ii) are not correct
🔗 Concept:
4.2
Does a Current Carrying Wire Get Hot?
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(c) Both (i) and (ii) are correct.
Explanation
Current heats the wire, so it becomes warm.
Current also makes a magnetic field, so the compass deflects.
So both effects happen at the same time.
One current shows both the heating and magnetic effects.

Q 4
Question
Match Column A with Column B: (i) Voltaic cell (ii) Electric iron (iii) Nichrome wire (iv) Electromagnet, with (a) best for electric heater (b) magnetic effect (c) heating effect (d) chemical reactions.
🔗 Concept:
4.2
Does a Current Carrying Wire Get Hot?
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(i)→(d), (ii)→(c), (iii)→(a), (iv)→(b).
Explanation
A Voltaic cell makes current by chemical reactions.
An electric iron works on the heating effect.
Nichrome wire is best suited for an electric heater.
An electromagnet works on the magnetic effect.
Each device is matched to the effect it works on.

Q 5
Question
Nichrome wire is commonly used in electrical heating devices because it:
(i) is a good conductor of electricity.
(ii) generates more heat for a given current.
(iii) is cheaper than copper.
(iv) is an insulator of electricity.
🔗 Concept:
4.2
Does a Current Carrying Wire Get Hot?
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(ii) It generates more heat for a given current.
Explanation
Nichrome has high resistance.
High resistance makes more heat for the same current.
So it is used in heating devices.
High resistance makes nichrome good for heating.

Q 6
Question
Electric heating devices are often considered more convenient than traditional methods like burning firewood or charcoal. Give reason(s) to support this, considering societal impact.
🔗 Concept:
4.2
Does a Current Carrying Wire Get Hot?
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Electric heating is cleaner, safer, and easier to control.
Explanation
Electric devices make no smoke, so the air stays clean.
This is better for health, especially indoors.
They are easy to switch on and off and control.
They do not need cutting trees for firewood.
Electric heating is clean, safe, and easy to use.

Q 7
Question
Look at Fig. 4.4a. If the compass near the coil deflects: (i) Draw an arrow to show the path of the current. (ii) Explain why the compass needle moves when current flows. (iii) Predict what happens to the deflection if you reverse the battery terminals.
🔗 Concept:
4.1.1
Electromagnets
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The current makes a magnetic field; reversing the terminals reverses the deflection.
Explanation
(i) The current flows from the positive terminal, through the coil, back to the negative terminal.
(ii) The current makes a magnetic field around the coil, which moves the compass needle.
(iii) Reversing the terminals reverses the current, so the needle deflects the other way.
Current makes the field; its direction sets the deflection direction.

Q 8
Question
Sumana forgets to switch off her lifting electromagnet. After some time, the nail no longer picks up clips, but the wire is still warm. Why did the lifting electromagnet stop lifting the clips? Give possible reasons.
🔗 Concept:
4.1.2
Lifting Electromagnets
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The cell has run down, so the magnetic field became too weak to hold the clips.
Explanation
The switch was left ON, so current flowed for a long time.
This used up the cell, so it became weak or dead.
A weak current makes a weak magnetic field, so the clips fall.
The wire is still warm from the heating effect of the current.
A run-down cell gives a weak field, so lifting stops.

Q 9
Question
In Fig. 4.11, beaker (a) has copper and iron in lemon juice, and beaker (b) has copper and iron in pure water. In which case will the LED glow when the switch is closed?
🔗 Concept:
4.3.1
Voltaic Cell
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The LED glows only in beaker (a), with lemon juice.
Explanation
Lemon juice is an electrolyte, so it helps make current.
So the cell in beaker (a) works and the LED glows.
Pure water is not a good electrolyte, so beaker (b) makes almost no current.
So the LED in beaker (b) does not glow.
An electrolyte like lemon juice is needed to make current.

Q 10
Question
Neha keeps the coil the same as in Activity 4.4 but slides the iron nail out, leaving only the coil. Will the coil still deflect the compass? If yes, will the deflection be more or less than before?
🔗 Concept:
4.1.1
Electromagnets
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Yes, it still deflects the compass, but the deflection is less.
Explanation
The coil with current is still a magnet on its own.
So it still deflects the compass needle.
But the iron core made the magnet stronger.
Without the nail, the magnet is weaker, so the deflection is less.
The coil still works, but is weaker without the iron core.

Q 11
Question
Four coils of similar shape and size are made from iron, copper, aluminium, and nichrome (Fig. 4.12), each connected to a cell. When current passes, near which coils will a compass needle deflect?
(i) Only in circuit (a)
(ii) Only in circuits (a) and (b)
(iii) Only in circuits (a), (b), and (c)
(iv) In all four circuits
🔗 Concept:
4.1
Does an Electric Current Have a Magnetic Effect?
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(iv) In all four circuits.
Explanation
All four metals are conductors, so current flows in each coil.
Any current carrying coil makes a magnetic field.
So the compass deflects near every coil.
The metal only changes how strong the effect is, not whether it happens.
Every current carrying coil deflects a nearby compass.

Make coils of 25, 50, 75, and 100 turns. Connect each to the same cell, one by one. Note the deflection of a compass kept in the same place each time. Draw a conclusion about how the number of turns affects the strength of the electromagnet.
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More turns make a stronger electromagnet.
Good Practices
Keep the cell and compass position the same each time.
Change only the number of turns.
Note the deflection for each coil.
You will see more turns give more deflection.
So more turns mean a stronger magnet.
Increasing the coil turns increases the magnet's strength.

Take two nichrome wires of equal length but different thickness. Pass current for 30 seconds in each and feel which heats more. Then repeat with two wires of the same thickness but different lengths. Write a brief report of your findings.
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Heat depends on the wire's thickness and length.
Good Practices
Use the same cell and the same time for each wire.
Touch each wire only for a moment, carefully.
Compare the thin and thick wires first.
Then compare the short and long wires.
Note which wire heats up more in each case.
The wire's thickness and length change how much it heats.

Try to make an electric cell using different fruits and vegetables. Also try electrodes made of different metals. See which combinations make the LED glow. Prepare a brief report of your results.
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Many juicy fruits and vegetables can work as electrolytes.
Good Practices
Use two different metals as electrodes, like copper and iron.
Try lemon, potato, tomato, and other juicy items.
Join several cells to get enough current.
Check if the LED glows for each combination.
Note which items work best.
Different metals with a juicy electrolyte can make a working cell.
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