Question

In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. What is the reading of the ammeter when the length of the wire is doubled ?

• A. 5 A
• B. 2 A
• C. 10 A
• D. 2.5 A

Answer 1

The correct option is D 2.5 A

Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter
$\rho$ (rho).
The SI unit of electrical resistivity is the ohm-metre
$(\Omega -m)$
As the resistance (R) is directly proportional to the length of the conductor, when the length is increased resistance increases and the current decreases.
The current through the circuit is 5A. That is, $I=\frac{V}{R}=5A$.
As the resistance is proportional to length, when the length is doubled, the resistance is also doubled. That is, $I^{\prime }=\frac{V}{2R}=2.5A$.
Hence, the reading in the ammeter is halved when the length of the conductor is doubled.