Quick questions on Magnetic force on moving charges and current-carrying conductors (QCE Physics Unit 3)

A charge $q$ moving with velocity $\vec{v}$ through a magnetic field $\vec{B}$ experiences a force:

Point your right hand's fingers in the direction of $\vec{v}$, curl them toward $\vec{B}$; the thumb points in the direction of $\vec{F}$ on a positive charge. For a negative charge (electron), reverse the direction.

A charge moving perpendicular to a uniform field experiences a constant-magnitude force always perpendicular to its velocity. The trajectory is a circle. Setting magnetic force equal to centripetal force:

A wire of length $L$ carrying current $I$ in a magnetic field $\vec{B}$ experiences a force:

Two long parallel wires carrying currents $I_1$ and $I_2$ separated by distance $d$ exert a force per unit length on each other:

A charged particle passing through perpendicular $\vec{E}$ and $\vec{B}$ fields experiences forces $qE$ and $qvB$. These can be made to cancel for a specific velocity:

Expect a velocity-selector or mass-spectrometer geometry with diagrams and a question on the radius of curvature, or a current-balance stimulus measuring the force between two parallel conductors. Right-hand-rule direction questions are routine.

A common IA2 design measures the force on a current-carrying conductor between the poles of a permanent magnet as a function of current (or wire length), and extracts the field strength $B$ from the slope. Strong reports linearise $F$ vs $I$ and report $B$ with uncertainty.

Maximum force occurs at $\theta = 90°$; parallel motion gives zero force.

It does not. Magnetic force is always perpendicular to velocity, so it does no work; the speed is constant in a uniform field.

$qvB$ is for a single moving charge; $BIL$ is for a wire carrying current. Do not double-count.

Same direction attracts, opposite direction repels. (The opposite is true for electric charges, which can confuse students.)