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Standard VIII
Physics
Resistivity
Question 5Use...
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Question 5
Use the data in Table to answer the following –

(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?

Table: Electrical resistivity of some substances at 20∘C
MaterialResistivity(Ωm)ConductorsSilver1.60×10−8Copper1.62×10−8Aluminium2.63×10−8Tungsten5.20×10−8Nickel6.84×10−8Iron10.0×10−8Chromium12.9×10−8Mercury94.0×10−8Manganese1.84×10−6AlloysConstantan(alloy of Cu Ni)49×10−6Manganin(alloy of Cu,Mn and Ni)44×10−6Nichrome(alloy of Ni,Cr,Mn and Fe)100×10−6InsulatorsGlass1010−1014Hard rubber1013−1016Ebonite1015−1017Diamond1012−1013Paper(dry)1012

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Solution

(a) Resistivity of iron = 10.0×10−8Ω m
Resistivity of mercury = 94.0×10−8Ω m
The resistivity of mercury is more than that of iron. This implies that iron is a better conductor than mercury.
(b) It can be observed from the table that the resistivity of silver is the lowest among the listed materials. Hence, it is the best conductor.

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Q. Question 5
Use the data in Table to answer the following –

(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?

Table: Electrical resistivity of some substances at 20∘C
MaterialResistivity(Ωm)ConductorsSilver1.60×10−8Copper1.62×10−8Aluminium2.63×10−8Tungsten5.20×10−8Nickel6.84×10−8Iron10.0×10−8Chromium12.9×10−8Mercury94.0×10−8Manganese1.84×10−6AlloysConstantan(alloy of Cu Ni)49×10−6Manganin(alloy of Cu,Mn and Ni)44×10−6Nichrome(alloy of Ni,Cr,Mn and Fe)100×10−6InsulatorsGlass1010−1014Hard rubber1013−1016Ebonite1015−1017Diamond1012−1013Paper(dry)1012
Q. The mode of the following data 8, 7, 9, 8, 7, 8, 10, 7, 10, 6, 7, 6, 10, 8, 6, 8 is ____
Q. Resistivity of some material is given below. State which one will be the best conductor.
MaterialCopperAluminiumSilverNickel
Resistivity (Ωm)1.62×10−82.63×10−81.60×10−86.84×10−8

Q. (a) What is meant by saying that the potential difference between two points is 1 volt? Name a device that helps to measure the potential difference across a conductor.
(b)Why does the connecting cord of an electric heater not glow hot while the heating element does?
(c) Electrical resistivities of some substances at 20°C are given below:
Silver 1.60 × 10−8 Ωm
Copper 1.62 × 10−8 Ωm
Tungsten 5.20 × 10−8 Ωm
Iron 10.0 × 10−8 Ωm
Mercury 94.0 × 10−8 Ωm
Nichrome 100 × 10−6 Ωm
Answer the following questions in relation to them:
(i) Among silver and copper, which one is a better conductor? Why?
(ii) Which material would you advise to be used in electrical heating devices? Why?
Q. The electrical resistivities of five substances A, B, C, D and E are given below:
A 5.20 × 10−8 Ω m
B 110 × 10−8 Ωm
C 2.60 × 10−8 Ωm
D 10.0 × 10−8 Ωm
E 1.70 × 10−8 Ωm

(a) Which substance is the best conductor of electricity? Why?
(b) Which one is a better conductor : A or C? Why?
(c) Which substance would you advice to be used for making heating elements of electric iron? Why?
(d) Which two substances should be used for making electric wires? Why?
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