$A$ thin hollow copper pipe carries a direct current. Which of the following statements is incorrect?

Two long conductors are arranged as shown above to form overlapping cylinders,each of radius $r$,whose centers are separated by a distance $d$. Current of density $J$ flows into the plane of the page along the shaded part of one conductor and an equal current flows out of the plane of the page along the shaded portion of the other,as shown. What are the magnitude and direction of the magnetic field at point $A$?

Write the equation for the magnetic field at an inside point of a very long solenoid.

Two wires with currents $3 \text{ A}$ and $1.5 \text{ A}$ are enclosed in a circular loop $P$. $A$ third parallel wire with current $1 \text{ A}$ is situated outside the loop as shown. All the wires are perpendicular to the plane of the circular loop. The value of $\oint \vec{B} \cdot d\vec{l}$ around the loop is ($\mu_0$ = permeability of free space) (in $\mu_0$)

$A$ closely wound solenoid of $80 \,cm$ long has $5$ layers of windings of $400$ turns each. The diameter of the solenoid is $1.8 \,cm$. If the current carried is $8 \,A$, then the magnitude of the magnetic field inside the solenoid near its centre is approximately

$A$ long straight wire of circular cross-section (radius $a$) is carrying steady current $I$. The current $I$ is uniformly distributed across this cross-section. The magnetic field is