"Science — How Things Work" — Practice

Question 1

A bulb connected in a circuit fails to glow even though the cell is fresh and the bulb is not burnt out. The most likely reason is:
(a) The circuit is closed  (b) The circuit is open somewhere along the loop  (c) The wires used are too thick  (d) The cell's positive and negative terminals are both working

Accepted Answer

A working cell and a working bulb will still fail to light if the conducting loop is broken anywhere — at a loose connection, an open switch, or a snapped wire — since current cannot flow through an incomplete loop.

Answer: (b) The circuit is open somewhere along the loop. Trap (a) is the opposite of what's happening — a closed circuit is exactly what would make the bulb glow, so it cannot be the reason it fails to. Trap (c) invents an irrelevant cause; wire thickness affects heating and resistance, not whether the circuit is complete. Trap (d) restates a condition that, if actually true alongside a genuinely closed loop, would make the bulb glow — it does not explain the failure described.

Question 2

Which of the following is used as an insulator around electrical wires specifically to prevent shocks?
(a) Copper  (b) Aluminium  (c) Rubber or plastic coating  (d) Iron

Accepted Answer

Rubber and plastic do not allow current to pass through them, which is exactly why wires are coated with one of these materials — to keep current confined to the metal core and prevent it reaching anyone touching the wire's outside.

Answer: (c) Rubber or plastic coating. Trap (a) Copper is the conductor typically used INSIDE the wire, not the protective coating around it — using it as insulation would defeat the purpose entirely. Trap (b) Aluminium is also a conductor, sometimes used for the wire core itself in some applications, but never as an insulating coating. Trap (d) Iron is a conductor and a magnetic material, neither of which makes it suitable as an insulating layer.

Question 3

A fuse in a household circuit 'blows' (melts) most commonly because:
(a) The voltage supplied is too low  (b) The current flowing through the circuit has exceeded a safe limit  (c) The fuse wire is made of a very high-melting-point metal  (d) The bulb connected to the circuit is switched off

Accepted Answer

A fuse is a low-melting-point wire in series with the circuit; when current exceeds the rated safe value — from a short circuit or an overloaded connection — it heats up quickly, melts, and breaks the circuit before damage occurs.

Answer: (b) The current flowing through the circuit has exceeded a safe limit. Trap (a) describes the opposite of the actual protective trigger — low voltage does not cause excess current or fuse-blowing in this way. Trap (c) reverses the fuse's design principle; it is deliberately made from a LOW-melting-point material so that it melts before other wiring is damaged. Trap (d) is unrelated — a switched-off bulb reduces current draw, if anything making a blown fuse less likely, not more.

Question 4

To increase the strength of an electromagnet made from a coil wound around a soft iron core, a student could correctly:
(a) Reduce the number of turns in the coil  (b) Increase the current flowing through the coil  (c) Replace the soft iron core with a wooden core  (d) Disconnect the battery briefly

Accepted Answer

Electromagnet strength increases with more coil turns, more current, and a soft iron (not non-magnetic) core — increasing the current is a direct, correct way to strengthen it.

Answer: (b) Increase the current flowing through the coil. Trap (a) reverses the correct relationship — reducing turns weakens, rather than strengthens, an electromagnet. Trap (c) replaces a magnetic core with a non-magnetic one, which would essentially eliminate the electromagnet's strength rather than increase it. Trap (d) would simply stop current flow altogether, removing the electromagnet's magnetism entirely rather than strengthening it.

Question 5

In a working electric bell, the hammer strikes the gong repeatedly as long as the bell push is held down because:
(a) A person must keep pressing the switch on and off rapidly by hand  (b) The armature's own movement repeatedly makes and breaks contact with the contact screw, restarting the cycle each time  (c) The battery alternates current direction automatically  (d) The gong itself vibrates the armature mechanically

Accepted Answer

The armature is attracted to the electromagnet, strikes the gong, and in doing so moves away from the contact screw — breaking the circuit, de-magnetising the core, letting the spring pull the armature back to remake contact and restart the whole cycle, entirely on its own once the bell push is held down.

Answer: (b). Trap (a) wrongly assumes the ringing depends on manual switching, when the self-interrupting armature-contact mechanism is exactly what makes a SINGLE held-down press produce continuous ringing. Trap (c) invents an alternating-current mechanism that has no role in this simple direct-current bell circuit. Trap (d) reverses cause and effect — the gong's vibration is the RESULT of the hammer's strike, not the cause of the armature's motion.

Question 6

A student tests four objects with a bar magnet. Which one would NOT be attracted?
(a) An iron nail  (b) A steel paperclip  (c) A cobalt sample  (d) A copper coin

Accepted Answer

Iron, steel (an iron alloy) and cobalt are all magnetic materials and would be attracted; copper, despite being a metal, is not attracted by a magnet.

Answer: (d) A copper coin. Trap (a) Iron is one of the three classic magnetic elements and would clearly be attracted. Trap (b) Steel, being largely iron, is also magnetic and commonly used in this exact classroom demonstration. Trap (c) Cobalt is the third of the three classic magnetic elements (along with iron and nickel) and would also be attracted.

Question 7

A teacher demonstrates magnetising a steel needle by winding a coil of insulated wire around it and passing current through the coil for a few minutes. This is an example of the:
(a) Single-touch method  (b) Double-touch method  (c) Electrical method  (d) Induction-by-contact method

Accepted Answer

Passing a strong current through a coil wound around a magnetic material is precisely the electrical method of magnetisation, generally producing the strongest and most uniform magnet of the standard methods.

Answer: (c) Electrical method. Trap (a) Single-touch involves stroking with one pole of an existing magnet repeatedly in one direction — no coil or current is involved. Trap (b) Double-touch involves stroking with two magnets simultaneously from the centre outward — again, no electric current is used. Trap (d) names a plausible-sounding but non-standard term; NCERT's three named methods are single-touch, double-touch, and the electrical method.

Question 8

A Class VII teacher has students physically connect a cell, wires, a bulb and a switch, and test several classroom objects with a homemade circuit tester, before ever showing them a circuit diagram. The strongest pedagogical justification for this sequencing is that:
(a) It is faster than teaching diagrams directly  (b) Concrete, directly observable, falsifiable experience is a more accessible entry point for young learners than abstract representation, in line with NCF 2005  (c) NCERT prohibits diagram-based teaching entirely  (d) Diagrams are no longer part of the syllabus once hands-on activities are used

Accepted Answer

NCF 2005's constructivist stance favours grounding abstract concepts (current, circuit, conductor) in concrete, hands-on, self-testable experience before introducing symbolic representation — the bulb lighting or not is a directly observable outcome a diagram alone cannot provide.

Answer: (b). Trap (a) misidentifies the justification as a matter of classroom time efficiency rather than pedagogical soundness — hands-on activities often take longer, not less time, than drawing a diagram. Trap (c) overstates NCERT's position; diagrams remain very much part of the syllabus and are taught, just typically after the hands-on foundation is built. Trap (d) is simply false — circuit diagrams continue to be taught and tested alongside hands-on activity, not replaced by it.

Question 9

A student, asked why a second bulb in a simple series circuit glows dimmer than the first, answers: "Because the current gets used up a little by the first bulb before it reaches the second one." This response reveals a misconception about:
(a) The difference between conductors and insulators  (b) The distinction between current (which is conserved around the loop) and energy (which is what is actually converted)  (c) The correct use of a fuse  (d) The direction of Earth's magnetic field

Accepted Answer

The student has correctly noticed that something changes as current passes through the first bulb, but has mislabelled it: current stays the same at every point of a simple series loop, while it is electrical energy that is progressively converted into heat and light — the classic 'current is used up' misconception this chapter specifically flags.

Answer: (b). Trap (a) is unrelated — the student's answer concerns what happens within an already-conducting circuit, not whether a material conducts at all. Trap (c) brings in an unrelated safety-device concept that plays no role in explaining relative bulb brightness. Trap (d) is entirely unconnected to this circuit-electricity scenario, drawing instead from the magnetism content in this same chapter.

Question 10

A compass needle, held far away from any other magnet, still consistently settles pointing north-south. This is best explained by:
(a) The needle has residual magnetism from its manufacturing process that fades over time  (b) Earth itself behaves like a giant magnet, and the needle aligns with its magnetic field  (c) The needle is attracted by the Sun's gravitational pull  (d) All compass needles are pre-set to point north-south and cannot rotate

Accepted Answer

A compass needle is a small, freely pivoted magnet, and it aligns with Earth's own magnetic field — present everywhere on the surface — without needing any other magnet nearby.

Answer: (b) Earth itself behaves like a giant magnet. Trap (a) invents a fading-magnetism explanation that doesn't account for the needle's reliably CONSISTENT north-south settling, which persists rather than fading. Trap (c) confuses a magnetic phenomenon with an unrelated gravitational one — gravity has no role in orienting a compass needle. Trap (d) contradicts the defining feature of a compass, which is precisely that its needle rotates freely and settles on its own, rather than being fixed in place.

Practice — "Science — How Things Work"

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