Resistance Geometry Relation — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Resistance Geometry Relation Applies to uniform conductors where the current density is assumed to be constant across the cross-section. Start with Ohm's Law: V = IR. Apply the definition of current: I = dQ dt = A I t . Substitute I into V = IR: V = R ( A I t ). Use the microscopic form of Ohm's Law: V = l A I. Equate the two expressions for V to find R: R = l A . 0 l 0 A > 0 Confusing resistance (R) with resistivity ( ); R depends on geometry, while is an intrinsic material property. Assuming resistance is proportional to the cross-sectional area A (it is inversely proportional). Forgetting that the units of resistivity are Ohm-meter ( m).