How Things Work — Electricity & Magnets (VI–VIII) • Topic 2 of 3

Conductors, Insulators & Effects of Current

CTET recap: Materials are sorted by whether they let an electric current pass. Conductors allow current to flow — almost all metals (copper and aluminium are common in wires), and also the human body, tap water and a moist surface. Insulators block current — rubber, plastic, dry wood, glass, ceramic and dry air. This is why electrical wires have a copper core (the conductor) wrapped in a plastic or rubber sheath (the insulator), and why a plug-top and switch cover are made of plastic. An electric current also produces three effects, which CTET tests by name: the heating effect (current heats a wire — used in an electric heater, iron, geyser and the filament of a bulb), the magnetic effect (current produces magnetism — a current-carrying wire behaves like a magnet, the principle of an electromagnet), and the chemical effect (current passing through a conducting solution causes chemical changes, as in electroplating). Pedagogy & how it's tested: The classic item gives a list of materials and asks which is a conductor or an insulator, or asks why wires are coated in plastic. The safety angle is common too — because the human body and water conduct, children must be taught never to touch switches with wet hands. Common misconceptions to flag: children think only thick or shiny things conduct; they assume all liquids (including pure/distilled water) conduct equally — in fact tap water conducts because of dissolved salts; and they confuse the heating effect with the bulb 'storing heat'. A good activity is the conductor-tester: complete a circuit with a tester and touch various objects to see which make the bulb glow.

✅ Solved examples

1. A child uses a circuit tester and finds the bulb glows when she touches a copper key but not a plastic comb. The copper key is a ____ and the plastic comb is an ____ :
Conductor and insulator respectively. Copper (a metal) lets current pass, so the bulb glows; plastic blocks current, so the bulb stays dark.
2. Electrical wires used in homes have a metal core covered with plastic. The plastic covering acts as:
An insulator. The copper core conducts the current while the plastic prevents current from passing to our hands, protecting us from shocks.
3. The heating of the coil in an electric heater is due to which effect of electric current?
The heating effect of electric current. When current passes through the resistance coil it gets hot and gives out heat.
4. Why are children warned never to touch an electric switch with wet hands?
Because the human body and water are conductors of electricity. Wet hands let current pass through the body easily, which can give a dangerous shock.

✏️ Practice — try these, take hints as needed

1. From the list — copper, rubber, iron, plastic — name the two insulators:
Insulators do NOT let current pass.
Metals are conductors.
Rubber and plastic
2. A current-carrying wire is found to deflect a nearby compass needle. This demonstrates the ____ effect of current:
It behaves like a magnet.
Basis of an electromagnet.
Magnetic effect
3. Electroplating a metal spoon with silver makes use of which effect of electric current?
Current through a solution causes a chemical change.
Chemical effect
4. Most metals, such as copper and aluminium, are good ____ of electricity:
Opposite of insulators.
They let current flow.
Conductors

📝 Topic test — 8 questions

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