First slide

Ohm's law

Question

Following figure shows cross-sections through three long conductors of the, same length and material, with square cross-section of edge lengths as shown. Conductor B will fit snugly within conductor A, and conductor C will fit snugly within conductor B. Relationship between their
end to end resistance is

Easy

A

R_A = R_B = R_C
B

R_A > R_B > R_C
C

R_A < R_B < R_C
D

Information is not sufficient

Solution

All the conductors have equal lengths. Area of cross-section of, A is $\{{(\sqrt{3} a)}^{2} - {(\sqrt{2} a)}^{2}\} = a^{2}$
Similarly area of cross-section of B - Area of cross-section of C = a²
Hence according to formula $R = ρ . \frac{l}{A};$ resistances of
all the conductors are equal i.e., R_A = R_B = R_C

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