Science — How Things Work — CTET Mathematics & Science

This chapter is really two NCERT chapters wearing one CTET name tag — the Class VI-VII current-electricity sequence (circuits, conductors, the heating and magnetic effects of current) and the Class VI magnetism chapter ("Fun with Magnets") — bundled together because both are, at bottom, about how a hidden physical cause produces a visible, testable effect: close a switch and a bulb lights, bring a magnet near a nail and it moves. CTET's questions lean on exactly that testability, which is also why this chapter's pedagogy angle — building real circuits with real cells and wires rather than only drawing them — is not a side note. It is the chapter's whole teaching philosophy in miniature.

1. What CTET actually asks

Science — How Things Work carries weightPct: 5 of the Mathematics & Science paper's 60 questions — roughly 3 questions, which works out to about 2-3 of the subject's ~30 Science-specific questions and up to 3 of the exam's 150 total marks. Every CTET question is marked +1 for a correct answer and 0 for a wrong or unattempted one — there is no negative marking anywhere on the paper, so a partially-remembered fact in this chapter is always worth acting on rather than leaving blank.

Questions in this chapter split roughly 70% content, 30% pedagogy. Content questions test the same facts a Class VII or VIII NCERT exam would: will this bulb light in this circuit, is this object a conductor, what makes a good electromagnet core, is a given material magnetic. Pedagogy questions test something adjacent but distinct: given a described classroom activity or a student's mistaken answer, can you recognise why NCERT teaches this topic the way it does, or what kind of misconception a student's wrong answer reveals. Both families draw on the same underlying content, so building the content foundation first (Sections 2-8) makes the pedagogy questions (Section 9) far more tractable than approaching them as a separate topic.

2. Electric current, simple circuits and circuit symbols

Electric current is a flow of electric charge. In a simple circuit, current flows from the cell's positive terminal, through the external circuit (wires, bulb, switch), back to the cell's negative terminal — this is the conventional direction used in circuit diagrams, and it is the direction CTET expects in any current-direction question at this level.

A simple circuit needs, at minimum, a source of electrical energy (a cell or battery, with two terminals marked + and −), connecting wires, and something for the current to do work on (commonly a bulb). A switch is a simple device inserted into the circuit purely to make or break the conducting path on demand, without disturbing the rest of the connections. The circuit is closed (complete) when there is an unbroken conducting loop from one terminal of the cell back to the other — current flows, and a connected bulb lights. The circuit is open the moment that loop is broken anywhere — at the switch, at a loose wire, inside a burnt-out bulb — and no current flows at all, anywhere in that loop.

NCERT's Class VI textbook introduces standard circuit symbols precisely so a circuit can be drawn on paper without sketching realistic cells and bulbs each time: a cell is a long thin line (positive terminal) next to a short thick line (negative terminal); a battery is simply two or more cells drawn in the same symbol, connected end to end; a bulb is a circle with a small cross or filament mark inside; a switch is shown as a break in the wire that can be shown open or closed; wires are plain straight lines joining components. Reading and drawing these symbols correctly — not just building physical circuits — is itself a testable skill, and a circuit-diagram question is really asking whether you can trace the loop on paper the same way you'd trace it with your finger on a real circuit board.

3. Conductors, insulators and testing materials

A conductor is a material that allows electric current to pass through it easily — most metals (copper, aluminium, iron) are good conductors, which is why connecting wires are made of metal. An insulator is a material that does not allow current to pass through it under normal conditions — rubber, plastic, dry wood, and glass are the standard NCERT examples, and this is exactly why wires are coated in plastic or rubber (to prevent current from escaping the wire and giving someone a shock) and why switches and plug bodies are made of plastic.

NCERT's classic hands-on activity for this section is building a simple circuit tester: a cell, a bulb, and two connecting wires with their free ends left loose, assembled so that touching the two loose ends together completes the circuit and lights the bulb. To test an unknown object, its two ends are inserted into the gap between the loose wire ends instead — if the bulb lights, the object is a conductor; if it stays dark, the object is an insulator. This turns an abstract classification (which materials conduct?) into a directly observable, repeatable test a student can run themselves rather than simply memorise from a list. A related nuance CTET occasionally tests: ordinary tap water (carrying dissolved salts and impurities) conducts current reasonably well and can complete a tester circuit, while pure or distilled water is a comparatively poor conductor — "water conducts electricity" is a useful classroom generalisation but not an absolute one.

4. The heating effect of current — appliances and the fuse

When current flows through a conducting wire, the wire offers some resistance to that flow, and this resistance converts part of the electrical energy into heat — this is the heating effect of electric current. How much heating occurs for a given current depends on the wire's material, length, and thickness: thinner and longer wires heat up more than thicker, shorter ones carrying the same current, which is why appliance-heating elements are deliberately made from thin, coiled, high-resistance wire rather than the same thick copper wire used for ordinary house wiring.

This effect is put to deliberate use in appliances built specifically to produce heat — the electric iron, room heater, toaster, and geyser all rely on the heating effect of current passing through a resistive element. Even an ordinary incandescent bulb glows because its thin tungsten filament heats up enough (tungsten is chosen for its very high melting point) to glow white-hot when current passes through it.

Unwanted or excessive heating is a fire and safety hazard, which is exactly why circuits include a fuse: a short length of thin wire, made from a metal or alloy with a deliberately low melting point, connected in series within the circuit (often in a separate fuse holder). If the current flowing through the circuit rises above a safe, rated limit — from a short circuit, an overloaded socket, or a faulty appliance — the fuse wire heats up quickly, melts, and breaks the circuit before the excess current can damage the wiring or start a fire. A blown fuse is therefore evidence of too much current, not too little, and must be replaced (or, in modern installations, reset via a miniature circuit breaker, an electronic/mechanical device that performs the same protective job without needing a physical wire to be replaced each time) only after the underlying fault is fixed.

5. The magnetic effect of current — electromagnets and the electric bell

A current-carrying wire is surrounded by a magnetic field — a fact discovered by Hans Christian Oersted, who noticed a nearby compass needle deflecting whenever current flowed through a wire placed close to it. This is the magnetic effect of electric current, and it is the working principle behind the electromagnet: an insulated wire wound into a coil around a core of soft iron. When current flows through the coil, the soft iron core becomes magnetised and behaves exactly like a magnet — attracting magnetic materials, showing a north and south pole — but the moment the current stops, the soft iron core loses almost all of its magnetism immediately. That instant on/off switchability, unlike a permanent magnet, is the electromagnet's defining and most useful property, which is also why the core must be soft iron and not steel — steel retains magnetism far more stubbornly once magnetised, which would defeat the purpose of a magnet meant to switch off on demand.

An electromagnet's strength can be increased three ways: increasing the number of turns of wire in the coil, increasing the current flowing through it, or using a soft iron core rather than air or a non-magnetic material inside the coil. Electromagnets appear throughout everyday and industrial technology — cranes that lift and drop scrap iron on command, loudspeakers, electric motors and generators, and, in hospitals, MRI machines.

The electric bell is NCERT's classic worked example combining the magnetic effect of current with make-and-break circuit action in a single, self-sustaining mechanism. Its parts: a battery, a bell push (switch), an electromagnet, a springy metal strip called the armature carrying a small hammer at one end, a contact screw the armature normally touches, and a gong. Pressing the bell push closes the circuit; current flows through the electromagnet's coil, magnetising its iron core, which attracts the armature toward it; the hammer, moving with the armature, strikes the gong, producing the familiar ring. But that same movement pulls the armature away from the contact screw — breaking the circuit at that contact point. With the circuit broken, the electromagnet instantly loses its magnetism (because it is an electromagnet, not a permanent one), and the springy armature snaps back to its resting position, remaking contact with the screw and closing the circuit again — at which point the whole cycle repeats. As long as the bell push is held down, this make-break-make cycle runs many times a second, producing continuous ringing rather than a single strike.

6. Magnets — natural vs artificial, and the properties of a magnet

Natural magnets occur in nature without any human intervention — the standard NCERT example is lodestone, a naturally magnetised form of the iron ore magnetite, typically weak in strength and irregular in shape. Artificial magnets are deliberately manufactured, given a defined shape suited to a specific purpose: the bar magnet, the horseshoe (U-shaped) magnet, cylindrical and ball-ended magnets, disc/ring magnets, and the slim magnetic needle used inside a compass.

Materials attracted by a magnet are called magnetic materials — iron, nickel, cobalt, and steel (an iron alloy) are the standard set. Materials not attracted are non-magnetic — wood, plastic, rubber, and paper are the obvious examples, but the trap CTET returns to repeatedly is that being a metal does not guarantee being magnetic: aluminium and copper are metals but are not attracted by a magnet, a distinction that separates "conducts electricity" (Section 3) from "is magnetic" (this section) as two genuinely independent properties, not two names for the same thing.

Every magnet, regardless of shape, shares the same core set of properties, and CTET tests each of these individually:

1. Attraction — a magnet attracts magnetic materials (iron, nickel, cobalt and their alloys), and only those materials.
2. Two poles — every magnet has a north (N) pole and a south (S) pole; attraction is strongest near the poles and weakest, effectively negligible, at the magnet's middle.
3. Like poles repel, unlike poles attract — two north poles (or two south poles) push each other apart; a north and a south pole pull toward each other.
4. Directional property — a magnet freely suspended or pivoted at its centre, so it can rotate without hindrance, always settles pointing in roughly the north-south direction. This single property is the entire basis of the compass (Section 8).
5. No isolated poles — break or cut a magnet into two pieces, and each piece becomes a complete, independent magnet with its own north and south pole; a single isolated N or S pole cannot be produced this way, however many times a magnet is divided.

7. Making, using and caring for magnets

An unmagnetised piece of magnetic material (a steel bar or needle, for instance) can be turned into an artificial magnet by several methods NCERT introduces as simple classroom activities:

• Single-touch method — one pole of a strong bar magnet is stroked repeatedly across the steel bar, always moving in the same direction and lifting the magnet clear before each return stroke; repeated stroking gradually magnetises the bar.
• Double-touch method — two magnets, with opposite poles facing the bar, are stroked simultaneously from the centre of the bar outward toward each end, magnetising it somewhat more evenly and quickly than the single-touch method.
• Electrical (current) method — an insulated wire is wound into a coil around the steel bar, and a strong direct current is passed through the coil for some time; this generally produces a stronger, more uniformly magnetised bar than either touch method, and connects directly back to the electromagnet principle of Section 5.

Magnets show up across everyday and technical uses: the compass for direction-finding, magnetic separators that pull iron scrap out of mixed waste for recycling, fridge-door magnetic seals and magnetic toys, loudspeakers and microphones, electric motors and generators, the magnetic stripe on ATM and bank cards, and MRI machines in hospitals.

Because a magnet's strength comes from the internal alignment of its magnetic domains, that alignment can be disturbed and the magnet weakened by rough handling: heat, hammering, and dropping are the three classic ways a magnet loses strength, and NCERT's care instructions follow directly from avoiding each of them. Bar magnets are conventionally stored in pairs, with unlike poles adjacent (a north pole next to a south pole), completing a closed magnetic loop, often with a soft-iron "keeper" piece bridging the free ends — this arrangement helps preserve the pair's strength during storage far better than leaving each magnet isolated. Magnets are also kept away from other magnets, magnetic materials, and sensitive electronic devices when not deliberately stored as a keeper pair, since stray magnetic fields can weaken a magnet or interfere with nearby equipment over time.

8. Earth's magnetism and the compass

The Earth itself behaves as though a giant (though comparatively weak) magnet were embedded within it — a phenomenon called Earth's magnetism or geomagnetism. This single fact explains why a magnetic needle, suspended or pivoted freely with nothing else nearby, still reliably settles pointing roughly north-south: it is aligning with Earth's own magnetic field, the same way any freely suspended magnet aligns with the field of a nearby stronger magnet (Section 6, property 4).

A compass is simply a small, lightweight magnetic needle mounted on a pivot so it can rotate freely in a horizontal plane. Wherever it is carried and however it is turned before being released, it settles back pointing north-south, letting a traveller read off direction reliably without any external landmark. Sailors and explorers have relied on this property for direction-finding at sea and across unfamiliar land for centuries — long before satellite navigation existed, the compass was the primary tool for staying on course, and it remains a standard, battery-free backup instrument today. At Class VII-VIII depth, CTET does not test magnetic declination or the distinction between true north and magnetic north — those are refinements for a later stage of schooling. The working idea to hold onto here is simply this: Earth's own magnetic field, not any hidden nearby magnet, is what makes a compass needle point north-south.

9. Pedagogy — hands-on circuit-building and common misconceptions

NCERT's treatment of current electricity is built around learning by doing, in line with NCF 2005's constructivist stance: students are expected to physically assemble a simple circuit from a cell, bulb, wires and a switch, and to test unfamiliar objects with a circuit tester, rather than only view a completed circuit diagram drawn on the blackboard. The reasoning behind this choice is worth knowing in its own right, because CTET treats it as a scoreable pedagogy fact: for a Class VI-VII learner, "current," "circuit" and "conductor" are abstract, invisible concepts, and a diagram alone asks the learner to trust an assertion about something they cannot see happening. A physically built circuit, by contrast, gives immediate, falsifiable feedback — the bulb either lights or it doesn't — and lets a learner debug their own misunderstanding through direct trial ("why isn't it lighting — is a wire loose, is the circuit actually closed?") rather than being told the correct answer outright. A teacher who has students build and test circuits with their own hands before introducing circuit diagrams is applying exactly this NCF-2005-endorsed sequence; a teacher who only ever draws diagrams on the board, however clearly, is not.

Two misconceptions recur often enough in real classrooms that CTET tests them directly, usually as a student's wrong answer embedded in a short scenario:

"Current gets used up as it goes around the circuit." This is false. In a simple series loop, the electric current is the same at every point around the circuit — what actually gets "used up," converted into heat, light, or another form of energy as current passes through a component like a bulb, is electrical energy, not the current itself. A student who holds this misconception will often predict that a second identical bulb, placed further along the same simple series loop, should glow dimmer than the first — a prediction a real circuit-building activity disproves directly, which is exactly why NCERT favours the hands-on version of this lesson.

Confusing series and parallel circuit behaviour. At an introductory level, the behaviour that matters is qualitative: in a series circuit, all components share one single loop, so if any one component fails (a bulb burns out, a wire disconnects), the entire circuit breaks and everything connected in that loop stops working. In a parallel circuit, each component has its own separate branch back to the source, so if one branch fails, the others keep working undisturbed — this is why household wiring is parallel (so one blown bulb doesn't switch off the whole house) while a cheap string of decorative lights wired in series famously goes fully dark the moment a single bulb fails. A student who assumes "one bulb failing always stops the whole circuit" is applying series-circuit logic to a parallel circuit, and vice versa.

11. Common traps

• Treating "current is used up" as literally true — current is conserved around a simple series loop; energy, not current, is what a component converts into another form.
• Assuming all conductors are also magnetic materials — copper and aluminium conduct electricity well but are not attracted by a magnet; conducting and being magnetic are independent properties.
• Using steel instead of soft iron for an electromagnet core — steel retains magnetism after the current stops, defeating the point of a switchable electromagnet; soft iron demagnetises almost instantly.
• Believing a broken magnet yields one isolated pole — every fragment of a broken magnet is a complete magnet with its own north and south pole.
• Reversing like-pole and unlike-pole behaviour — like poles repel, unlike poles attract; this reverses easily under exam pressure if not drilled as a fixed pair.
• Assuming the electric bell rings continuously because someone is repeatedly pressing the switch — the continuous ringing comes from the armature's own self-interrupting make-break contact with the screw, not repeated manual switching.
• Confusing "series circuit failure = total failure" with parallel circuit behaviour, or vice versa — a broken series loop stops everything in that loop; a broken parallel branch stops only that branch.
• Assuming a compass needle points north-south because of a hidden nearby magnet — it aligns with Earth's own magnetic field, which exists everywhere on the surface, not because of a local magnet.
• Mixing up which method (single-touch, double-touch, electrical) is being described in a scenario question — read for whether one magnet or two is used, and whether current is involved, before choosing.

12. Revision protocol

Build the content foundation first — one pass covering circuits and current (Sections 2-4) and one covering magnetism (Sections 6-8), each anchored to a small set of testable facts rather than free-floating definitions: what makes a circuit closed versus open, what a fuse actually protects against, what soft iron gives an electromagnet that steel doesn't, and the five core properties every magnet shares. Only once those facts are solid does the pedagogy layer (Section 9) become fast to answer, because most pedagogy questions here are really content questions wearing a classroom-scenario disguise — a student's wrong answer, decoded, is almost always one of the two misconceptions in Section 9. With zero negative marking, commit to an answer on every question in this chapter, even a half-remembered one: eliminating even one obviously wrong option (an aluminium object attracting a magnet, a steel core for a switchable electromagnet) already tilts a guess in your favour.