Answer:
Length of the wire = 145.84 m
Step-by-step explanation:
Given : You wish to use #18 tungsten wire at 20°C to make a 10 Ω resistor.
To find : Length of wire will be required for this job.
Solution :
The #18 tungsten has a radius of
.
The resistivity of the tungsten at 20° is
.
The formula that relates resistance and resistivity is

where L is the length of the wire, R is the resistor,
its section and
is the resistivity .
Now, we can calculate L :





Therefore, Length of the wire = 145.84 m