Question

15. Electrical resistivities of some substances, in ohmmeter, at 200 C are given as follows:



Silver 1.60 x 10-8

Copper 1.62 x 10-8

Tungsten 5.2 x 10-8

Mercury 94 x 10-8

Iron 10 x 10-8

Nichrome 10 x 10-6

a) Out of the silver and copper, which is a better conductor of electric current and why?

b) A resistance wire made from german silver has a resistance of 4.25 ohms. Calculate the

resistance of another wire, made for the same material, such that its length increases by 4

times and area of cross -section decreases by 3 times. ( 4 x 1 =4)

c) Why are conductors of electric heating devices, such as toasters and electric irons made

of an alloy rather than a pure metal?

d) Why is tungsten used almost exclusively for filament of incandescent lamps? ​

Answer 1

Electrical resistivities of some substances, in ohm-meter, at 20°C are given as follows : 

(a) Out of the silver and copper, which is a better conductor of electric current and why ? 

(b) Which substance is preferred to be used for electrical transmission lines ? Give reason.

 (c) Name the material that you would advise to be used in the heater elements of electric heating device and why ? 

answer

(a) Silver is a better conductor, lower resistivity.

 (b) Copper, economical / low resistivity.

 (c) Nichrome; Very high resistivity / as it is an alloy, it does not oxidize readily at high temperature.

Answer 2

Answer:

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