Current Electricity and Electrical InstrumentHard
Question
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 resistivity of Al and Fe are 2.7 × 10-8 W m and 1.0 × 10-7 Wm, respectively. The electrical resistance between the two faces P and Q of the composite bar is :
Options
A.
B.
C.
D.
Solution
case-1
Aluminium
A = (72 - 22) = 45 mm2
ρ = 2.7 × 10-8 Ωm
l = 50 mm
R1 =
R1 = 30 μΩ
case-2
Ferrous
A = 4 mm2
ρ = 10-7 Ωm
l = 50 mm
R2 =
R2 = 1250 μΩ
Rnet =
Rnet =
μΩ
∴ (B)
Aluminium
A = (72 - 22) = 45 mm2
ρ = 2.7 × 10-8 Ωm
l = 50 mm
R1 =
R1 = 30 μΩ
case-2
Ferrous
A = 4 mm2
ρ = 10-7 Ωm
l = 50 mm
R2 =
R2 = 1250 μΩ
Rnet =
Rnet =
μΩ∴ (B)
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