The electrical resistivity of three materials A, B and C at 20°C is given below :
Generated by claude-sonnet-4-6 · 2026-06-15 06:45 · grounding rag
Model Answer
(i) Classification:
- A (resistivity = $10^{17}$ Ω m) → Insulator
- B (resistivity = $44 × 10^{-6}$ Ω m) → Alloy
- C (resistivity = $1.62 × 10^{-8}$ Ω m) → Conductor
(ii) Examples and uses:
| Material | Example | Use in Electric Stove/Iron |
|----------|---------|---------------------------|
| Insulator (A) | Rubber / Ebonite | Used as outer covering/handle of electric iron to prevent electric shock. |
| Alloy (B) | Manganin / Nichrome | Used as heating element (coil) in electric iron/stove because alloys have high resistivity and don't oxidise easily at high temperatures. |
| Conductor (C) | Copper | Used as connecting wires to carry current with minimum energy loss due to very low resistivity. |
Source: Chapter 11 – Electricity, Section 11.5 (Table 11.2)
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Explanation
- Resistivity range tells you the category: ~$10^{12}$–$10^{17}$ Ω m = insulator; ~$10^{-6}$ Ω m = alloy; ~$10^{-8}$ Ω m = conductor (metal).
- Examiners expect you to match the given values to Table 11.2 — C ($1.62 × 10^{-8}$) matches Copper exactly.
- For uses, always link the property (high resistivity → heating element; low resistivity → connecting wire; insulator → protective cover) to the function. This fetches full marks.