Discover, Design and Debate — Projects — "Electricity: Magnetic and Heating Effects"

1. 15 marksCuriosity Grade 8, Chapter 4, page 61, project 1

   Make coils of 25, 50, 75 and 100 turns. Connect them to the same cell one by one and note the deflection of a magnetic compass placed in the same position each time. Report your observations and draw a conclusion about the effect of the number of turns on the strength of an electromagnet.

   Hint. The phrase 'in the same position' is the whole design of this experiment.

   How to run it fairly. The one thing you are changing is the number of turns, so everything else must be held still:

   • The same cell, and a fresh one — a cell that weakens as you work through the four coils would make the later coils look worse than they are. Connect only for a few seconds each time.
   • The same wire, of the same thickness, wound on cylinders of the same diameter.
   • The same compass, in the same position — mark its outline on the table in pencil and put it back on the mark every time. Deflection depends strongly on distance, so a compass that creeps closer would fake the result.
   • No iron core in any of them, or the same nail in all four.
   • Let the needle settle back to north–south between trials.

   Recording. Make a table before you start, not after:

   Number of turns	Deflection (degrees)	Trial 2	Trial 3
   25
   50
   75
   100

   Read the deflection off the compass scale rather than writing 'a little' or 'a lot', and repeat each coil two or three times so you can see how much your readings wobble.

   ✦ The conclusion you should expect. The deflection increases as the number of turns increases, because every turn carries the same current and every turn adds its own magnetic effect, so the effects add up. This confirms the chapter's statement that the increase in number of turns of the coil also makes the coil a stronger magnet.

   Report honestly. If two of your readings come out the same, or one is out of order, write down what you got and say so. Small differences in winding tightness, in the compass position and in reading a scale by eye are enough to blur the pattern between 75 and 100 turns. An experiment reported as it happened is worth more than one tidied up to match the expected answer.

2. 24 marksCuriosity Grade 8, Chapter 4, page 61, project 2

   Take two thin nichrome wires of equal length but different thickness (about 0.3 mm and 0.6 mm). Connect them one by one in a circuit with a switch and a cell, and let the current flow for 30 s in each case. Touch the wires momentarily. Which wire heats up more?

   Hint. The chapter lists thickness among the factors the heat depends on — but does not tell you which way round.

   Safety first, before anything else. This is a heating experiment, so it follows the rules of Activity 4.5: do it under a teacher's supervision, touch the wire only momentarily, do not hold it, and let it cool before handling the circuit.

   The design. Equal lengths, equal time (30 s), same cell, same switch — the only difference is the thickness, which is what makes the comparison meaningful.

   What to expect. The thinner wire (0.3 mm) heats up more than the thicker one (0.6 mm). A thinner wire of the same material and length offers a higher resistance to the current, and it is that resistance which converts electrical energy into heat. The thinner wire also has less material to spread the heat through, so the same heat raises its temperature further.

   ✦ What the chapter does and does not tell you here. It says only that the heat generated in a wire depends on the material, thickness, length of the wire, and the duration for which the current flows. It does not say which of the two thicknesses wins. That is exactly why this is set as a project rather than a comprehension question — you are expected to find out by doing it, not to look the answer up. Run the experiment, record what you feel, and let the result stand.

   Reporting. Since 'warm' and 'hot' judged by hand are rough measures, describe carefully what you felt, say how long after switching off you touched each wire, and swap the order of the two wires on a second run to check that the result is not an artefact of which one you tried first.

   Connect to everyday life. This is why household wiring for a heavy appliance is thicker than the flex on a table lamp: a thin wire carrying a large current gets hot, which is precisely the danger the chapter's 'A step further' box on ratings warns about.

3. 34 marksCuriosity Grade 8, Chapter 4, page 61, project 2

   Repeat the same activity with two nichrome wires of the same diameter but of different lengths. Prepare a brief report.

   Hint. Now length is the variable and thickness is held fixed — the mirror image of the last experiment.

   The design. Same nichrome, same thickness, same cell, same 30 s — only the length differs. Together with the previous experiment this isolates the two geometrical factors one at a time, which is the only way to say what each one does.

   The same safety rules apply: teacher's supervision, momentary touch, no holding the wire.

   What to look for, and how to judge it. This one is more subtle than the thickness experiment, and the reason is worth understanding. A longer wire of the same thickness offers more resistance, which reduces the current in the circuit — and less current means less heat produced. But the longer wire also has more surface over which any heat it does produce is spread out. So there are two effects working against each other, and the result is not obvious in advance.

   ✦ This is genuinely an experiment, not a demonstration. The chapter gives no prediction for this case, and neither will this answer. Do it, feel both wires, and report what you actually found — including 'I could not tell the difference' if that is the truth. Deciding in advance what the answer must be, and then reporting that, is the one thing that would spoil the exercise.

   What a brief report should contain:

   Section	What goes in it
   Aim	What you set out to find
   Materials	Wire material, both lengths, thickness, cell, switch
   Method	What you did, including the 30 s and where you touched
   Observations	What each wire felt like, in your own words
   Conclusion	What you can and cannot conclude from it
   Sources of error	Judging temperature by hand; different cooling times; a cell that weakened between trials

   The last row is not padding. Two wires touched a few seconds apart, or judged by a hand that has just held a warm wire, can easily be reported wrongly.

4. 44 marksCuriosity Grade 8, Chapter 4, page 61, project 3

   Try to make an electric cell using various fruits and vegetables. Also try electrodes of different metals. Prepare a brief report.

   Hint. You are testing two separate ideas here — the electrolyte and the electrode pair.

   Two experiments, not one. Keep them apart or you will not be able to say what caused what.

   Experiment A — change the electrolyte. Keep the electrode pair fixed (copper wire and iron nail, as in Activity 4.6) and try different fruits and vegetables: lemon, orange, tomato, potato, apple, cucumber. Use the same number of units joined in a chain each time, and the same LED.

   Experiment B — change the electrodes. Keep the fruit fixed and try different metal pairs. The chapter's list of pairs used in Voltaic cells is a good place to start: zinc/copper, zinc/silver, aluminium/copper, iron/copper, magnesium/copper, and lead/copper. A galvanised (zinc-coated) nail and a copper wire is the easiest pair to find. Remember that the two electrodes must be of different metals and must not touch inside the fruit.

   ✦ What you are really testing. Activity 4.6 might leave the impression that something about lemons produces electricity. These two experiments take that idea apart. If other fruits work as well, the lemon was never special — it was only supplying an acidic liquid to act as the electrolyte. And if changing the metals changes the result while the fruit stays the same, the metals matter too. That is Volta's own conclusion, reached by your own hands: it was the combination of metals and liquid that generated electric current.

   Practical notes. Roll and squeeze a fruit before use so the juice moves freely. Clean the metals before each trial, since a dirty surface can stop a working cell from working. If the LED does not glow, reverse it before deciding the cell has failed. And since a single unit is weak, join several in a chain as Fig. 4.8b shows.

   Reporting. Tabulate fruit against metal pair and record whether the LED glowed, and how brightly. Say which combinations failed as well as which succeeded — a combination that does not work is a result, and it is the failures that tell you what a cell actually needs.

   Do not eat anything used in these experiments.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity, Textbook of Science for Grade 8, Chapter 4 'Electricity: Magnetic and Heating Effects', book pages 46-61 (hecu104.pdf, 16 pages, Reprint 2026-27), downloaded from ncert.nic.in and read page by page. Every activity number, figure number, quantity and quoted sentence below was checked against that PDF. Figures read at high resolution: Fig. 4.4a (compass, coil ends A and B, and cell polarity - the cell's - terminal is on the left and + on the right, and the red north tip of the needle has swung towards end A, so end A is the south pole for the connections shown); Fig. 4.12 (a: iron nail and copper strip in lemon juice, b: same electrodes in pure water); Fig. 4.13 (four coils of iron, copper, aluminium and nichrome, each with a cell and a switch). Three deliberate restraints on what is claimed. (1) The chapter gives the heating effect entirely qualitatively - 'the heat generated depends on the magnitude of the electric current' and on 'the material, thickness, length of the wire, and the duration' - and gives no formula. No formula is supplied here either; Joule's law, Ohm's law, power and kWh belong to a later grade and appear nowhere in this book. (2) The two wire-heating projects are answered as experiments to be performed, not as results to be reproduced: the thickness comparison is explained, and the length comparison is explicitly left open because two effects work against each other and the chapter offers no prediction. (3) Solid-state batteries are reported in the chapter's own tense - under development, advantages expected - and the lithium and cobalt supply question is described without naming countries or quantities, since the chapter names none.. Questions are referenced from the NCERT textbook for identification.