If an observer is moving with respect to a stationary electron,then he observes:

What is the $SI$ unit of permeability?

$A$ charged particle enters a uniform magnetic field perpendicular to its initial direction,travelling in air. The path of the particle is seen to follow the path in the figure. Which of the statements $1-3$ is/are correct?
$[1]$ The magnetic field strength may have been increased while the particle was travelling in air.
$[2]$ The particle lost energy by ionising the air.
$[3]$ The particle lost charge by ionising the air.

$A$ and $B$ are two parallel conductors carrying a current $i$ in the same direction. $x$ and $y$ are two electron beams moving in the same direction as shown in the figure.

Two concentric loops $A$ and $B$ of same radius $R = 2 \pi \,cm = 2 \pi \times 10^{-2} \,m$ are placed at right angles to each other. If the currents flowing through $A$ and $B$ are $I_A = 3 \,A$ and $I_B = 4 \,A$ respectively, then the net magnetic field at their common centre is:

$A$ rectangular coil carrying current is placed in a non-uniform magnetic field. On that coil, the total: