Moving Charges and Magnetism Questions

When a charged particle moving with velocity $\vec{v}$ is subjected to a magnetic field of induction $\vec{B}$, the force on it is non-zero. This implies that:

Two circular coils $1$ and $2$ are made from the same wire but the radius of the $1^{\text{st}}$ coil is twice that of the $2^{\text{nd}}$ coil. What is the ratio of the potential difference applied across them so that the magnetic field at their centres is the same?

A proton carrying $1\text{MeV}$ kinetic energy is moving in a circular path of radius $R$ in uniform magnetic field. What should be the energy of an $\alpha$ -particle to describe a circle of same radius in the same field?

Two similar coils of radius $R$ are lying concentrically with their planes at right angles to each other. The currents flowing in them are $I$ and $2I$, respectively. The resultant magnetic field induction at the centre will be: