Arrange the following in terms of their dielectric strength in ascending order: (A) Bakelite (B) Mica (C) Paper (impregnated) (D) Teflon Choose the correct answer from the options given below:
(A), (C), (D), (B)
Understanding Dielectric Strength of Materials
Dielectric strength is a crucial property of insulating materials. It represents the maximum electric field strength that a material can withstand without breaking down, i.e., becoming conductive. It is typically measured in volts per unit thickness, such as kilovolts per millimeter (kV/mm).
We are asked to arrange four common insulating materials — Bakelite, Mica, Impregnated Paper, and Teflon — in ascending order based on their dielectric strength.
Dielectric Strength Values for Common Insulators
Let's look at the typical ranges of dielectric strength for each material:
| Material | Symbol | Typical Dielectric Strength Range (kV/mm) |
|---|---|---|
| Bakelite | (A) | 15 - 30 |
| Mica | (B) | 50 - 200 (varies by type, Muscovite is high) |
| Paper (impregnated) | (C) | 40 - 60 (for oil-impregnated paper) |
| Teflon (PTFE) | (D) | 50 - 100 |
Comparing Dielectric Strengths
Based on these typical ranges, we can compare the materials:
- Bakelite has the lowest range ($\approx 15-30$ kV/mm).
- Impregnated Paper has a higher range than Bakelite ($\approx 40-60$ kV/mm).
- Teflon and Mica have significantly higher ranges ($\approx 50-100$ kV/mm for Teflon, and $\approx 50-200$ kV/mm for Mica). Mica, especially Muscovite Mica, can have the highest dielectric strength among these materials.
Arranging these from the lowest typical value to the highest typical value:
- Bakelite (A): Lowest range.
- Paper (impregnated) (C): Higher than Bakelite.
- Teflon (D): Higher than Impregnated Paper.
- Mica (B): Can be higher than Teflon, especially high-quality mica.
Arranging in Ascending Order of Dielectric Strength
Following the comparison, the ascending order of dielectric strength is:
Bakelite < Paper (impregnated) < Teflon < Mica
Which corresponds to the order of symbols:
(A), (C), (D), (B)
Final Answer Derivation
Comparing the derived order (A), (C), (D), (B) with the given options, we find the correct sequence.
Revision Table: Insulating Material Properties
| Material | Dielectric Strength ($\text{kV/mm}$) | Common Uses |
|---|---|---|
| Bakelite | 15 - 30 | Electrical switches, handles, appliance casings |
| Mica | 50 - 200 | High-temperature insulation, capacitors, heating elements |
| Paper (impregnated) | 40 - 60 | Capacitors, transformer insulation |
| Teflon (PTFE) | 50 - 100 | High-frequency insulation, wiring, gaskets |
Additional Information: Factors Affecting Dielectric Strength
Several factors can influence the measured dielectric strength of an insulating material:
- Thickness: Dielectric strength often decreases with increasing thickness.
- Temperature: High temperatures can reduce dielectric strength.
- Moisture: Absorption of moisture significantly lowers dielectric strength for many materials (especially paper and Bakelite).
- Frequency: For AC fields, frequency can affect dielectric strength.
- Shape of Electrodes: The geometry of the test electrodes and the presence of sharp points can influence breakdown voltage.
- Presence of Impurities: Contaminants can create weak points leading to premature breakdown.
The values provided are typical ranges, and specific values can vary depending on the exact composition, manufacturing process, and environmental conditions.
Important Questions from Classification of Materials
Pure graphite contains
Which statement about Curie point is correct?
Arrange the following in ascending order of their dielectric constant:
(A) Si 3N 4
(B) Ge
(C) GaAs
(D) SiO 2
Choose the correct answer from the options given below:
What type of magnetic behaviour is observed in a type I superconductor?
________ is a copper-free alloy.
