1) The resistivity of potentiometer wire is 40 x 10-8 ohm -metre and its area of cross-section is 8 x 10-6 m2 ,If 0.2-ampere current is flowing through the wire , then the potential gradient of the wire is A) 10−1 V/m B) 10−2 V/m C) 10−3 V/m D) 10−4 V/m Answer: Option BExplanation:Given , ρ=40×10−8 Ωm A= 8×10−6m2; l= 0.2 A as resistance is given as R= ρlA ∴ Rl=ρA=40×10−88×10−6=5×10−2 The potential gradient of the were is Vl=lRl=0.2×5×10−2=10−2V/m
