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Questions
On what factors does the resistance of a conductor depend?
List the factors on which the resistance of a uniform cylindrical conductor of a given material depends.
List two factors on which the resistance of a rectangular conductor depends.
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Solution
Factors on which the resistance of a conductor depends:
- Length of conductor: Resistance is directly proportional to the length of the conductor. This means Resistance increases with an increase in the length of the conductor. This is the cause that long electric wires create more resistance to the electric current.
- Area of cross-section: Resistance is inversely proportional to the area of the cross-section of the conductor. This means Resistance will decrease with an increase in the area of the conductor and vice versa. This is the cause that thick copper wire creates less resistance to the electric current.
- Temperature: Resistance is directly proportional to the temperature.
- Nature of material: Some materials create the least hindrance and hence are called good conductors. Silver is the best conductor of electricity. While some other materials create more hindrance in the flow of electric current, i.e. flow of electrons through them. Such materials are called bad conductors. Bad conductors are also known as insulators. The hard plastic is one of the best insulators of electricity.
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RELATED QUESTIONS
Use the data in the Table given below to answer the following –
Which among iron and mercury is a better conductor?
Table give below Electrical resistivity of some substances at 20°C
| Electrical resistivity of some substances at 20°C | ||
| − | Material | Resistivity (Ω m) |
| Conductors |
Silver | 1.60 × 10−8 |
| Copper | 1.62 × 10−8 | |
| Aluminium | 2.63 × 10−8 | |
| Tungsten | 5.20 × 10−8 | |
| Nickel | 6.84 × 10−8 | |
| Iron | 10.0 × 10−8 | |
| Chromium | 12.9 × 10−8 | |
| Mercury | 94.0 × 10−8 | |
| Manganese | 1.84 × 10−6 | |
| Alloys |
Constantan (alloy of Cu and Ni) |
49 × 10−6 |
| Manganin (alloy of Cu, Mn and Ni) |
44 × 10−6 | |
| Nichrome (alloy of Ni, Cr, Mn and Fe) |
100 × 10−6 | |
| Insulators | Glass | 1010 − 1014 |
| Hard rubber | 1013 − 1016 | |
| Ebonite | 1015 − 1017 | |
| Diamond | 1012 − 1013 | |
| Paper (dry) | 1012 | |
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What would be the effect on the resistance of a metal wire of:
increasing its length?
What would be the effect on the resistance of a metal wire of:
increasing its diameter?
What would be the effect on the resistance of a metal wire of:
increasing its temperature?
How does the resistance of a wire change when:
its material is changed to one whose resistivity is three times?
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Resistance of a metal wire of length 5 m is 100 Ω . If the area of cross - section of the wire is `3 × 10^-7 "m"^2` , Calculate the resistivity of the metal .
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The element used almost exclusively for filaments of incandescent lamps:
How will the resistance of a wire be affected if its
- length is doubled, and
- radius is also doubled ?
Give justification for your answer.
