29. (a) What is electrical resistivity? In a series
electrical circuit comprising of a resistor
having a metallic wire, the ammeter reads 5
A. The reading of the ammeter decreases to
half when the length of the wire is doubled.
Why?
Answers
Answer:Electrical resistivity is a measure of how strongly a particular material opposes the flow of electric charges.It is electric resistance per unit length per area of cross section of the material.It is also called as specific resistance of a conductor. Its SI unit is ohm*meter.Resistivity does not depend upon area of cross section and length of the conductor, but depends upon the nature of the conductor.Metals have low resistivity, while alloys have very high resistivity.
The ammeter reading is decreased to half because Resistance of a wire is directly proportional to the length of the wire.So, when the length gets doubled, the length increases, therefore, the resistance also increases , making less current to flow through the wire.
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Answer:
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Ans. The inherent property of a conductor because of which it resists the flow of electric current is called resistivity. Resistivity for a particular material is unique
Resistance varies directly as length of the conductor.
Current varies inversely as resistance.
So, when length of the wire is doubled, its resistance becomes double. When resistance becomes double, current becomes half.
This explains why the reading of ammeter decreases to half when the length of the wire is doubled.