Question

If the resistance of a certain copper wire is 1 ohm, then the resistance of a similar nichrome wire will be about :
Choose the option 25 ohm
30 ohm
60 ohm
45 ohm

Answer 1

At 20°C :

Copper resistivity = 1.75 x 10**-8 ——————————-> R = 1 Ohm

Ni 80 Cr 20 alloy resistivity = 1.05 x 10**-6 —————→ R = 60 Ohms

Ni 60 Cr 12 Fe 28 alloy resistivity = 1.20 x 10**-6 ———-> R = 68 Ohms

Ni 30 Al 65 Cr 5 alloy resistivity = 1.40 x 10**-6 ———→ R = 80 Ohms

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Answer 2

Given :

As we know that

R= ρ l/ A

Resistivity of copper = 1.7 x 10 ⁻⁸ Ω m

Resistivity of Nichrome =1.1 x 10⁻⁶ Ω m

Resistance of coppe wire = 1 ohm

R= ρ l/ A

R/ ρ  = l/A

l/A= 1/  1.7 x 10 ⁻⁸   =58.82x 10 ⁶

For Nichrome =

R=ρ l/ A= 1.1 x 10⁻⁶ x 58.82 x 10⁶

=64.735 ohm

So nearest option is C