Which of the following particle will describe the smallest circle when projected with the same  velocity perpendicular to the magnetic field ?

An electron emitted by a heated cathode and accelerated through a potential difference of $ 2.0 \;kV$, enters a region with uniform magnetic field of $0.15\; T$. Determine the trajectory of the electron if the field

$(a)$ is transverse to its initial velocity,

$(b)$ makes an angle of $30^o$ with the initial velocity

A magnetic field

Two particles $A$ and $B$ having equal charges $+6\,C$, after being accelerated through the same potential difference, enter in a region of uniform magnetic field and describe circular paths of radii $2\,cm$ and $3\,cm$ respectively. The ratio of mass of $A$ to that of $B$ is

The direction of magnetic force on the electron as shown in the diagram is along

A proton moving with a velocity, $2.5 \times {10^7}\,m/s$, enters a magnetic field of intensity $2.5\,T$ making an angle ${30^o}$ with the magnetic field. The force on the proton is