NEET 2022 — Physics solution

NEET2022Physics

A copper wire of length 10 m and radius $(1 0^{- 2} / π)$ m has electrical resistance of 10 $Ω$ . The current density in the wire for an electric field strength of 10 (V/m) is:

A
$1 0^{6}$ A/m $^{2}$
B
$1 0^{- 5}$ A/m $^{2}$
C
$1 0^{5}$ A/m $^{2}$
D
$1 0^{4}$ A/m $^{2}$

Solution

Cross-sectional area: $A = π r^{2} = π (\frac{1 0 ^{- 2}}{π})^{2} = 1 0^{- 4}$ m $^{2}$ .

Voltage across wire from field: $V = E ℓ = 10 \times 10 = 100$ V.

Current: $I = V / R = 100/10 = 10$ A.

Current density: $j = I / A = 10/1 0^{- 4} = 1 0^{5}$ A/m $^{2}$ .

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