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In an aluminum (Al) bar of square cross section, a square hole is drilled and is filled with iron (Fe) as shown in the figure. The electrical resistivities of Al and Fe are 2.7 × 10 –8 Ω m and 1.0 × 10 –7 Ω m, respectively. The electrical resistance between the two faces P and Q of the composite bar is Fe 2mm P Q Al 50 mm 7mm

1. Ω μ 64 2475
2. Ω μ 64 1875
3. Ω μ 49 1875
4. Ω μ 132 2475

Correct answer: Ω μ 64 1875

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