RRB Technician Grade I 19 Dec 2024 Shift 3 Paper

Concept:The ampere is defined using the magnetic force acting between two parallel current-carrying conductors.Explanation:The SI unit of electric current is the ampere, symbol $A$.According to the SI definition, one ampere is that constant current which, when maintained in two straight, parallel conductors of infinite length and negligible cross-section placed $1$ metre apart in vacuum, produces a force of $2 \times 10^{-7}$ newton per metre of length between them.When current flows through a conductor, it produces a magnetic field around it.Two parallel current-carrying conductors interact through their magnetic fields, producing a force between them.This force is attractive if the currents flow in the same direction and repulsive if they flow in opposite directions.The force per unit length is given by $F/L = \frac{\mu_0 I_1 I_2}{2\pi d}$, where $\mu_0 = 4\pi \times 10^{-7}\, \text{N/A}^2$ is the permeability of free space, $I_1$ and $I_2$ are the currents in the conductors, and $d$ is the distance between them.Thus, the ampere is defined based on the force between two current-carrying conductors, not on magnetic flux, potential difference, or the force between charges.Answer:Option A: the force between two current-carrying conductors.