Which one of the following particles cannot be accelerated by a cyclotron?

A proton and an alpha particle enter in a uniform magnetic field with the same velocity. The period of rotation of the alpha particle will be

An electron and a proton have equal kinetic energies. They enter a magnetic field perpendicularly, then

Two particles $X$ and $Y$ have charges $q$ and $4 q$ respectively. After being accelerated through the same potential difference, they enter a region of uniform magnetic field and describe circular paths of radii $\mathrm{R}$ and $\frac{\mathrm{R}}{2}$ respectively.
The ratio of mass of $X$ to that of $Y$ is

Which of the following is a CORRECT statement?

A straight wire of length $0.5 \mathrm{m}$ carrying a current of $1.6 \mathrm{ampere}$ is placed in a uniform magnetic field of induction $2 \mathrm{T}$. If the magnetic field is perpendicular to the length of the wire, then force on the wire is

A current of $10 \mathrm{ampere}$ is flowing in a wire of length $1.5 \mathrm{m}$. A force of $15 \mathrm{N}$ acts on it when it is placed in a uniform magnetic field of $2 \mathrm{tesla}$. The angle between the magnetic field and the direction of the current is

No force acts on a current carrying conductor in a magnetic field when angle between current and magnetic field is

The strength of the magnetic field at a point distant $r$ near a long straight current carrying wire is $B$. The field at a distance $\frac{r}{2}$ will be