On your first day at work as an electrical technician, you are asked to determin

Question

On your first day at work as an electrical technician, you are asked to determine the resistance per meter of a long piece of wire. The company you work for is poorly equipped. You find a battery,a voltmter, and an ammeter,but no meter for directly measuring resistance (an ohmmeter). You put the leads from ther voltmeter across the terminals of the battery, and the meter roads 12.0 V. You cut off a 20.0 m length of wire and connect it to the battery, with an ammeter in series with it to measure the current in the wire. The ammeter reads 6.90 A. You then cut off a 40.0-m length of wire and connect it to the battery again with the ammeter in series to measure the current. The ammeter in series to measure the current. Even though the equipment you have available to you is limited, your boss assures you have avialable to you is limited, your boss assures you of its high quality. The ammeter has very small resistance, and the voltmeter has large resistance.

Explanation / Answer

voltage of battery =12 v

from first observation,

V=IR

12 = 6.9* R

R=1.74

the resistnce of 1 m wire is 1.74/20=0.087 ohm/m

from 2nd observation,

V=IR

12 = 4.2* R

R=2.86

the resistnce of 1 m wire is 2.86/40=0.071 ohm/m

the resistnce of 1 m wire is (0.071+0.087)/2= 0.079 ohm/m

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