A very long straight conducting wire, lying along the $z$-axis, carries a current of $2 \mathrm{A}$. The integral $\int \overrightarrow{B}.d\overrightarrow{\ell }$ is computed along the straight line $\mathrm{PQ}$, where $\mathrm{P}$ has the coordinates $(2 \mathrm{cm}, 0, 0)$ and $\mathrm{Q}$ has the coordinates $(2 \mathrm{cm}, 2 \mathrm{cm}, 0)$. The integral has the magnitude (in $\mathrm{T} \mathrm{m}$)