Activity 4.1 — Electric Current and the Compass Needle — "Electricity: Magnetic and Heating Effects"

1. 13 marksCuriosity Grade 8, Chapter 4, pages 47-48, Activity 4.1

   List the materials needed for Activity 4.1 and describe how the circuit is set up. Why is the middle portion of the longer wire stretched between two nails, slightly above the surface of the cardboard?

   Hint. Look at what has to fit underneath that stretched piece of wire.

   Materials. A magnetic compass, an electric cell, a cell holder, two drawing pins, a safety pin, two nails, two pieces of connecting wire (one longer and one shorter), and two small pieces of cardboard.

   Setting it up.

   1. Make a switch from the two drawing pins, the safety pin and a piece of cardboard — the same switch built in Electricity: Circuits and their Components, Curiosity Grade 7.
   2. Put the cell in the cell holder.
   3. Fix the two nails to the second piece of cardboard and stretch the middle part of the longer wire between them, so that it runs straight and clear of the cardboard (Fig. 4.1a).
   4. Join one end of that wire to the cell holder and the other end to the switch.
   5. Join the shorter wire between the cell holder and the switch, completing the circuit.
   6. Place the magnetic compass beneath the stretched wire, between the two nails.

   ✦ Why the wire is raised on nails. The compass has to sit directly under the wire and as close to it as possible, because the magnetic effect is strongest near the wire. Stretching the wire between two nails leaves a clear gap for the compass to be slipped underneath, and it also keeps that stretch of wire straight and fixed. That matters: if the wire were free to move it might be nudged by hand while you switch on, and you would not be able to tell whether the needle moved because of the current or because the wire shifted.

   So the arrangement is doing two jobs at once — getting the detector close enough, and removing an obvious source of doubt about what caused the movement.

2. 23 marksCuriosity Grade 8, Chapter 4, page 48, Activity 4.1

   What do you observe about the compass needle when the switch is moved to the 'ON' position? What do you observe when it is moved back to 'OFF'? What happens when you repeat this a few times?

   Hint. Watch the needle the whole time, not just before and after.

   Switch ON. As soon as current begins to flow through the wire, the compass needle deflects — it swings away from the north–south direction it had been resting in.

   Switch OFF. The current stops and the needle returns to its original direction, settling back along north–south.

   Repeating it. The needle deflects and returns, deflects and returns, every single time — reliably, and in step with the switch.

   ✦ Why the repetition is the important step. A needle that moved once might have been disturbed by a passing magnet, a knock on the table, or a draught. A needle that moves only when you close the switch and returns only when you open it, over and over, cannot be explained that way. The repetition is what turns a single observation into evidence, which is why the activity asks for it explicitly.

   Notice also that the needle does not stay deflected after the current stops. The effect is not something the wire acquires and keeps — it lasts exactly as long as the current does.

3. 33 marksCuriosity Grade 8, Chapter 4, page 48

   Why does the compass needle deflect when current flows through the wire?

   Hint. What is a compass needle made of, and what makes it move?

   Because the current-carrying wire produces a magnetic field, and the compass needle is a magnet.

   The reasoning runs in three steps, and the chapter builds it from what was learnt in Exploring Magnets, Curiosity Grade 6:

   1. The compass needle is a tiny magnet. It normally rests along north–south, and it deflects whenever a magnet is brought near it.
   2. That magnetic influence acts through non-magnetic materials placed in between — so the cardboard and air are no obstacle.
   3. Here no magnet has been brought near it — only a current has been switched on. Yet the needle deflects. So the current-carrying wire must itself have a magnetic effect on the needle.

   ✦ And the effect belongs to the current, not the wire. When the current stops, the magnetic effect disappears and the needle swings back. The same piece of wire does nothing at all when no current is passing through it.

   This is the whole discovery of the chapter in one sentence: an electric current produces a magnetic field.

4. 42 marksCuriosity Grade 8, Chapter 4, page 48

   What is meant by a magnetic field? Give the chapter's definition.

   Hint. The definition is written in terms of what you could detect, not what you can see.

   Definition. The region around a magnet or a current carrying wire where its magnetic effect can be felt, such as by the deflection of a compass needle, is said to have a magnetic field.

   Two things worth noticing about how this is worded.

   • It is defined as a region of space, not as an object. The field is not the magnet and not the wire; it is the space around them in which the effect shows up.
   • It is defined by a test you can actually perform — bring a compass needle into the region and see whether it deflects. The field itself is invisible, so it is described through its detectable effect.

   ✦ The same definition covers both sources. A bar magnet has a magnetic field around it, and so does a wire carrying a current. That is exactly why a compass cannot tell you, by itself, which of the two is nearby — it reports only that it is sitting in a magnetic field.

5. 53 marksCuriosity Grade 8, Chapter 4, page 48

   State the magnetic effect of electric current.

   Hint. State it in the book's own words, then say what happens when the current stops.

   The statement. When electric current flows through a conductor (like a wire), it produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current. The magnetic field disappears when the current stops flowing.

   Unpacking it.

   Part of the statement	What it commits you to
   any conductor	It is not special to iron wire or to coils — a plain straight copper wire does it too
   produces a magnetic field around it	The field is in the space surrounding the wire, not confined to the wire
   disappears when the current stops	The effect is temporary and is tied to the current, not to the wire

   ✦ A useful way to hold it in mind: a wire with a current in it behaves, for as long as the current lasts, a bit like a magnet — and stops the moment the current does. That is why the effect can be switched, which no permanent magnet allows.

   The chapter lists the practical uses that follow from this one fact: electromagnets, electric bells, motors, fans and loudspeakers. Every one of them exists because a current can be turned on and off at will, and the magnetism follows it.

6. 65 marksCuriosity Grade 8, Chapter 4, page 48, Be a scientist

   Read the 'Be a scientist' box about Hans Christian Oersted. What did he notice, what did he do about it, and what did other scientists do next? What does this sequence tell you about how science works?

   Hint. There are three distinct stages here — and the third one is not Oersted's doing.

   Who he was. Hans Christian Oersted (1777–1851), a professor at a university in Denmark. His discovery was made in 1820.

   The three stages.

   Stage	What happened
   Noticing	It is said that while giving a demonstration he noticed that whenever an electrical circuit was closed or opened, the needle of a magnetic compass lying nearby deflected
   Investigating	He did not stop at the chance observation. He investigated it, and only when he was certain that an electric current really did produce a magnetic field did he publish his findings
   Checking	Other scientists repeated his experiment to see whether they got the same results, and then went further into the connection between electricity and magnetism

   ✦ What the sequence shows. A chance observation is the beginning of a discovery, not the discovery itself. Oersted's compass could have twitched for a dozen ordinary reasons; what made it science was that he tested it until he was sure, and then made the claim public so that other people could try to reproduce it. A result that no one else can obtain does not survive.

   And you have just done the same experiment. The chapter says so directly — in Activity 4.1 you made the same discovery Oersted made, which is why the box is headed Be a scientist rather than A great scientist.

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.