Page 24 - CHAPTER-1 (Electricity)

CHAPTER 1

ELECTRICITY

Bonus Round

Resistivity

• It is defined as the resistance of a conductor of unit length and

unit area of cross-section.

• Its SI unit is ohm-meter (Ω-m).

• The resistivity of a material is independent of its length or

thickness but depends on the nature of the substance and

temperature.

• It is a characteristic property exhibited by the material of the

conductor and varies only if its temperature changes.

• Insulators such as glass, rubber, ebonite, etc., have a very high

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resistivity (10 to 10 Ω-m), while conductors have very low
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resistivity (10 to 10 Ω-m).
• Alloys have relatively higher resistivity than that of their

constituent metals.

• They do not oxidise easily at high temperatures; this is why they

are used to make up most of the heating elements of devices

such as electric iron, heaters, etc.

• Tungsten is almost used exclusively for filaments of electric

bulbs, whereas copper and aluminum are generally used for

electrical transmission lines.

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