A proton, a deutron and an $\alpha$-particle accelerated through the same potential difference enter a region of uniform magnetic field, moving at right angles to it. What is the ratio of their kinetic energy?

A wire is bent in the form of an equilateral triangle of side $100 \mathrm{cm}$ and carries a current of $2 A.$ It is placed in a magnetic field of induction $2.0 T$ directed perpendicular into the plane of paper. The direction and magnitude of magnetic force acting on each side of the triangle will be