NEET 2020 Model Question Paper 4

Here, Length of each rod, l = 1 m
Area of cross-section of each rod,
A=0.01cm2=0.01×10−4m2
Resistivity of copper rod,
ρcu=1.7×10−6Ωcm
=1.7×10−6×10−2Ωm =1.7×10−8Ωm
Resistivity of iron rod,
ρcu=10−5Ωcm=10−7Ωm
∴ Resistance of copper rod,
RCu=ρCu

l

A

And resistance of iron rod, RFe=ρFe

l

A

As copper and iron rods are connected in series, therefore equivalent resistance is
R=RCu+RFe =ρCu

l

A

+ρFe

l

A

=(ρCu+ρFe)

l

A

Voltage required to produce 1 A current in the rods is
V=IR=(1)(RCu+RFe)
=(ρCu+ρFe)

l

A

=(1.7×10−8+10−7)(

1

0.01×10−4

)V
=10−7(0.17+1)(106)V
=1.17×10−1V=0.117V