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JEE Main202122 Jul 2021Morning ShiftPhysicsCurrent ElectricityActual

A Copper ( Cu ) rod of length 25 cm and cross-sectional area 3 mm 2 is joined with a similar Aluminium ( Al ) rod as shown in figure. Find the resistance of the combination between the ends A and B . (Take resistivity of Copper = 1 . 7 × 10 - 8 Ωm , Resistivity of aluminium = 2 . 6 × 10 - 8 Ωm )

Options

  1. A2 . 170   mΩ
  2. B1 . 420   mΩ
  3. C0 . 0858   mΩ
  4. D0 . 858   mΩ

Correct answer

D. 0 . 858   mΩ

Step-by-step solution

R = R 1 R 2 R 1 + R 2 = ℓ A · ρ 1 ρ 2 ρ 1 + ρ 2 R = 25 × 10 - 2 3 × 10 - 6 × 1 . 7 × 2 . 6 × 10 - 16 4 . 3 × 10 - 8 R = 0 . 858   mΩ

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