Question

The electrical resistivity of three materials A, B, and C at 20°C is given below: 
Material A: Resistivity \(10^{17} \Omega \, {m}\) 
Material B: Resistivity \(44 \times 10^{-6} \Omega \, {m}\) 
Material C: Resistivity \(1.62 \times 10^{-8} \Omega \, {m}\) 
(i) Classify these materials as conductor, alloy, and insulator. 
(ii) Give one example of each of these materials and state one use of each material in the design of an electrical appliance, say an electric stove or an electric iron.

Hint:

The materials with high resistivity are used as insulators, while those with low resistivity are used as conductors for electricity.

Answer 1

(i) Classification:
Material A with resistivity \(10^{17} \Omega \, {m}\) is an insulator, as its resistivity is extremely high, preventing the flow of electricity.
Material B with resistivity \(44 \times 10^{-6} \Omega \, {m}\) is an alloy, which has moderate resistivity and is often used in electrical heating applications.
Material C with resistivity \(1.62 \times 10^{-8} \Omega \, {m}\) is a conductor, as it has low resistivity, allowing electricity to flow easily.
(ii) Examples and Uses:
Material A (Insulator): Example - Rubber, Glass. 
Use: Insulating materials like rubber are used for covering wires to prevent electric shock. 
Material B (Alloy): Example - Nichrome (used in heating elements). 
Use: Nichrome is used in electric stoves and heating elements due to its ability to withstand high temperatures. 
Material C (Conductor): Example - Copper, Silver. 
Use: Copper is used in electrical wires due to its excellent conductivity.