The resistance of a very fine aluminum wire with a 20 μm × 20 μm square cross section is 1200 Ω . A 1200 Ω resistor is made by wrapping this wire in a spiral around a 2.3-mm-diameter glass core.How many turns of wire are needed?

Respuesta :

Explanation:

The given data is as follows.

         Resistance (R) = 1200 ohm,     Area (A) = [tex]20 \times 10^{-6}[/tex] m (as [tex]1 \mu m = 10^{-6} m[/tex])

            Diameter (d) = 2.3 mm = [tex]2.3 \times 10^{-3}[/tex] m

First, we will calculate the length as follows.

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

Here,  [tex]\rho[/tex] = resistivity of aluminium = [tex]2.65 \times 10^{-8}[/tex]

Putting the given values above and we will calculate the value of length as follows.

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

             1200 = [tex]2.65 \times 10^{-8} \times \frac{L}{20 \times 10^{-6}}[/tex]

               L = [tex]9.056 \times 10^{5}[/tex]

As the circumference of circular wire = [tex]2 \pi r[/tex]

or,                                                          = [tex]2 \times \pi \times \frac{d}{2}[/tex]  

                                                              = [tex]\pi \times d[/tex]

And, number of turns will be calculated as follows.

             No. of turns × Circumference = Length of wire

              No. of turns × [tex]3.14 \times 2.3 \times 10^{-3} = 9.056 \times 10^{5}[/tex]

                               = [tex]1.25 \times 10^{8}[/tex]

Thus, we can conclude that [tex]1.25 \times 10^{8}[/tex]  turns of wire are needed.

The number of turns of wire that should be required is 2506.

Calculation of the number of turns of wire:

Here we know that

The resistance of the wire should be

R = Resistivity of material * length / cross-sectional area

So,

Length = AR / P

= (20*10^-6)^2 * 1200 / 2.65 * 10^-8

= 18.1 m

Now the circumference of the circle should be

= 2πr

= 2π (2.3*10^-3)/2

= 7.22 *10^-3 m

Now the no of loop should be

= 18.1/7.22*10^-3

= 2506 turns

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