Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Conductors: Materials that allow electric current to flow through them easily are called conductors. They have a large number of free electrons. Examples include metals like Silver (), Copper (), and Aluminum ().
Insulators: Materials that do not allow electric current to flow through them are called insulators or non-conductors. They lack free electrons. Examples include Rubber, Plastic (PVC), Glass, and Ebonite.
Free Electrons: In conductors, the outermost electrons are loosely bound to the nucleus and can move freely within the material, facilitating the flow of charge ().
Resistance (): It is the opposition offered by a substance to the flow of electric current. Conductors have very low resistance, while insulators have infinitely high resistance.
Human Body and Earth: The human body is a conductor of electricity, which is why we get electric shocks. The Earth is also a good conductor, used in safety 'earthing' systems.
Electrolytes: Certain liquids like salt solution () or dilute acids conduct electricity due to the movement of ions rather than free electrons.
Semiconductors: Materials like Silicon () and Germanium () have electrical conductivity between that of a conductor and an insulator.
📐Formulae
💡Examples
Problem 1:
A current of flows through a copper wire when a potential difference of is applied. Calculate the resistance of the wire. Is the wire a conductor or an insulator?
Solution:
Given: , . Using Ohm's Law: .
Explanation:
Since the resistance is very low (), the copper wire allows current to flow easily and is therefore a conductor.
Problem 2:
Why are electrical wires usually coated with Plastic or PVC ()?
Solution:
PVC is an insulator with extremely high resistance.
Explanation:
Insulators do not allow the flow of electric current. Coating wires with PVC prevents the current from escaping the wire and protects users from accidental electric shocks if they touch the wire.
Problem 3:
Explain why distilled water is an insulator but tap water is a conductor.
Solution:
Distilled water is pure and lacks ions. Tap water contains dissolved salts like and .
Explanation:
Conduction in liquids requires ions. Pure distilled water has no free ions to carry charge, making it an insulator. Tap water contains dissolved minerals that dissociate into ions, allowing the flow of electricity.