An engineer cuts a 1.0-m-long, 0.33-mm-diameter piece of wire, connects it across a 1.5 V battery, and finds that the current in the wire is 8.0 A.
Find the resistitvity rho of the piece of the wire.

Respuesta :

Answer:

The resistivity of the wire is:

[tex]\rho=1.60\,\,10^{-8}\,\,\Omega\,m[/tex]

Explanation:

Recall the formula that connects resistance R with the material's resistivity [tex]\rho[/tex] :

[tex]R=\frac{\rho\,\,L}{A}[/tex]

where A stands for the cross-sectional area of the wire, and L for the wire's length.

In our case, the cross-sectional area of a 0.33 mm wire is the area of a circle of 0.165 mm radius (0.000165 m) which we can calculate as:

[tex]A=\pi\,\,R^2=\pi\,\,0.000165^2\,\,m^2=8.55\,\,10^{-8} \,\,m^2[/tex]

Since we don't have the actual resistance, but the information on the current on the wire when applying a potential difference, we use Ohm's Law to get the resistance R of the wire:

[tex]V=I\,\,R\\1.5 = 8 \,\, R\\R = \frac{1.5}{8} \, \Omega\\R= 0.1875\,\,\Omega[/tex]

Now, using the resistance formula shown at the beginning, we solve for the resistivity [tex]\rho[/tex] :

[tex]R=\frac{\rho\,\,L}{A}\\0.1875\,\,\Omega=\frac{\rho\,\,(1\,\,m)}{(8.55\,\,10^{-8}\,m^2)}\\\rho=0.1875\,*\,8.55\,\,10^{-8}} \,\,\Omega\,m\\\rho=1.60\,\,10^{-8}\,\,\Omega\,m[/tex]

The resistivity rho of the piece of the wire will be "1.60 × 10⁻⁸ Ωm".

Ohm's Law

According to the question,

Voltage, V = 1.5 V

Current in a wire, I = 8.0 A

Diameter of a wire= 0.33 mm

Length or a wire = 1.0 m

We know,

The area of circle,

A = πR²

By substituting the values,

  = π × 0.000165²

  = 8.55 × 10⁻⁸ m²

By using Ohm's Law,

→ V = IR

By substituting the values,

1.5 = 8 R

  R = [tex]\frac{1.5}{8}[/tex]

     = 0.1875 Ω

We know that,

→      R = [tex]\frac{\rho L}{A}[/tex]

By substituting the values,

0.1875 = [tex]\frac{\rho \times 1 \ m}{8.55\times 10^{-8}}[/tex]

hence,

Material's resistivity will be:

       ρ = 0.1875 × 8.55 × 10⁻⁸

          = 1.60 × 10⁻⁸ Ωm

Thus the above answer is right.

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