Which of the following materials is a good insulator?

1. Analyze the question

The question asks you to identify which of the listed materials is a "good insulator." In physics, an insulator is a material that resists the flow of electric current because its electrons are tightly bound to their atoms and are not free to move.

2. Explain the concept

• Conductors: These are materials that allow electric current to flow through them easily. They have "free electrons" that move freely throughout the material. Metals like silver, copper, and aluminum are excellent conductors.
• Insulators: These are materials that do not allow electric current to flow through them. They have very few or no free electrons. Examples include rubber, glass, plastic, and dry wood.
• Water: Pure water is a poor conductor, but the water we encounter in daily life (tap water, rain water) contains dissolved minerals and salts, which makes it a conductor.

3. Show the solution

• Option A (Silver): Silver is a metal and is actually the best conductor of electricity among all metals. Therefore, it is not an insulator.
• Option B (Water): As mentioned, water (especially tap water) contains ions that allow electricity to pass through it. It is considered a conductor in most practical scenarios.
• Option C (Rubber): Rubber has a very high electrical resistance. It does not allow electrons to flow through it, which is why it is used to coat electrical wires to prevent shocks. It is a classic example of an insulator.
• Option D (Copper): Copper is the most common material used for electrical wiring in our homes because it is a very good conductor of electricity.

4. Identify the answer

Comparing the options, Rubber is the only material listed that prevents the flow of electricity.

5. Exam Tip

When you see questions about conductors and insulators, remember the "Free Electron Rule": If the material has free electrons, it is a conductor (metals). If it holds its electrons tightly, it is an insulator (non-metals like rubber, plastic, or glass).