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What are conductors and insulators of electricity?

Class 7 ScienceNCERT chapter: Electricity: Circuits and their Componentsइसे हिंदी में पढ़ें

Exam-ready answer

Materials that allow electric current to pass through them are called conductors of electricity, such as copper, aluminium, iron and other metals. Materials that do not allow electric current to pass through them are called insulators, such as plastic, rubber, glass and dry wood. Electric wires use a metal conductor inside and an insulating plastic covering outside.

Explanation

Materials can be tested with a simple tester: a cell, a bulb and wires joined in a circuit with a gap between two free ends. When an object is placed across the gap, the bulb glows only if the object lets current pass. A steel spoon, an iron nail, aluminium foil and a copper wire make the bulb glow. A plastic scale, a rubber eraser, a glass bangle and a dry wooden stick do not.

So most metals are conductors, while plastic, rubber, glass, dry wood and paper are insulators. There is an interesting exception: pencil lead, made of graphite, a form of carbon, also makes the tester bulb glow, although carbon is a non-metal. Both kinds of materials are useful. Copper and aluminium carry current in wires, while plastic and rubber coverings stop the current from reaching our hands.

Our body is also a conductor, and so is ordinary tap water, because it contains dissolved salts; pure distilled water is a poor conductor. That is why switches and appliances must never be touched with wet hands, and electricians use tools with rubber or plastic handles. These facts explain why plugs, switchboards and wire coverings are made of insulating materials.

Points to remember

  1. Conductors: materials that allow electric current to pass through them, e.g. copper, aluminium, iron, silver.
  2. Insulators: materials that do not allow electric current to pass, e.g. plastic, rubber, glass, dry wood, paper.
  3. Most metals are good conductors; graphite (pencil lead) is a non-metal that also conducts electricity.
  4. An electric tester (cell, bulb and wires with a gap) shows whether a material conducts electricity.
  5. The human body and tap water conduct electricity, so electrical devices must never be handled with wet hands.

Exam tip

Give two lists with at least three examples each, and add one safety use, such as the plastic covering on wires, to show why the difference between conductors and insulators matters.

Questions students also ask

Why are electric wires covered with plastic?
The copper or aluminium inside the wire carries the current. The plastic covering is an insulator, so current cannot pass from the wire to a person touching it or to another wire. This prevents electric shocks and short circuits.
Is water a conductor or an insulator?
Pure distilled water is a poor conductor of electricity. Tap water, pond water and sea water contain dissolved salts, so they conduct electricity. That is why wet hands and wet floors increase the risk of an electric shock.
Why do electricians use screwdrivers with plastic or rubber handles?
Plastic and rubber are insulators. The handle stops electric current from passing from the metal tip into the electrician's hand, which protects them from an electric shock while working on wires and switches.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.