An electric field of $1500\, V / m$ and a magnetic field of $0.40\, weber / meter^2$ act on a moving electron. The minimum uniform speed along a straight line the electron could have is

A proton and an $\alpha$ -particle, having kinetic energies $K _{ p }$ and $K _{\alpha},$ respectively, enter into $a$ magnetic field at right angles.

The ratio of the radii of trajectory of proton to that of $\alpha$ -particle is $2: 1 .$ The ratio of $K _{ p }: K _{\alpha}$ is :

A particle of mass $'m'$ and carrying a charge $'q'$ enters with a velocity $'v'$ perpendicular to a uniform magnetic field. The time period of rotation of the particle

Fill the blank :

$(i)$ Static charge produces …… field around it.(Electric, Magnetic)

$(ii)$ Moving charge produces …… field around it.

A proton and an $\alpha – $particle enter a uniform magnetic field perpendicularly with the same speed. If proton takes $25$ $\mu \, sec$ to make $5$ revolutions, then the periodic time for the $\alpha – $ particle would be……..$\mu \, sec$