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प्रश्न
What do you understand by the "resistivity" of a substance?
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उत्तर
We know that resistance , `R=(rhol)/A`
So resistivity, `rho=RA/l/`
When the area of cross-section, A is 1 m2 and the length of the wire, l is 1 m, resistance is equal to resistivity.
Resistivity may be defined as the resistance offered by a conductor of length 1 m and area of cross-section 1 m2.
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संबंधित प्रश्न
On what factors does the resistance of a conductor depend?
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10−8Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?
Which of the following are conductors and which are insulators?
Sulphur, Silver, Copper, Cotton, Aluminium, Air, Nichrome, Graphite, Paper, porcelain, Mercury, Mica, Bakelite, Polythene, Manganin.
What is the general name of the substances having infinitely high electrical resistance?
Distinguish between good conductors, resistors and insulators. Name two good conductors, two resistance and two insulators.
What is meant by the "resistance of a conductor" ? Write the relation between resistance, potential difference and current.
Which has more resistance:
a thick piece of nichrome wire or a thin piece?
What will be the resistance of a metal wire of length 2 metres and area of cross-section 1.55 × 10−6 m2 if the resistivity of the metal be 2.8 × 10−8 Ω m?
Give two examples of substances which are good conductors of electricity. Why do you think they are good conductors of electricity?
How does the resistance of a conductor depend on:
length of the conductor?
How does the resistance of a conductor depend on:
area of cross-section of the conductor?
How does the resistance of a conductor depend on:
temperature of the conductor?
How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistors R1, R2 and R3 in series connected to a battery of V volts?
The effective resistance between A and B is:
A cylindrical conductor of length l and uniform area of cross-section A has resistance R. Another conductor of length 2l and resistance R of the same material has an area of cross-section:
Assertion: Conductors allow the current to flow through themselves.
Reason: They have free charge carriers.
Use the data in the Table given below to answer the following –
Which material is the best 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 | |
