During a laboratory experiment, a student finds
that at 20° celsius, a 6.0-meter length of copper
wire has a resistance of 1.3 ohms. the crosssectional
area of this wire is
(1) 7.9 × 10^−8 m2 (3) 4.6 × 10^0 m2
(2) 1.1 × 10^−7 m2 (4) 1.3 × 10^7 m2

ρ = resistivity of copper at 20 °C = 1.72 x 10⁻⁸ ohm-m

R = resistance of the copper wire = 1.3 ohm

L = length of the copper wire = 6 meter

A = area of cross-section of the copper wire = ?

Resistivity of copper wire is given as

R = ρL/A

inserting the values in the above equation

1.3 = (1.72 x 10⁻⁸) (6)/A

A = 7.9 x 10⁻⁸ m²

Hence the correct choice is

(1) 7.9 x 10⁻⁸ m²

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