How does the strength of the magnetic field at the centre of a circular coil of wire depend on: $(i)$ the radius of the coil $(ii)$ the number of turns of wire in the coil $(iii)$ the strength of the current flowing in the coil?

(N/A) The magnetic field $B$ at the centre of a circular coil is given by the formula $B = \frac{\mu_0 NI}{2R}$,where $N$ is the number of turns,$I$ is the current,and $R$ is the radius.
$(i)$ The magnetic field is inversely proportional to the radius of the coil $(B \propto \frac{1}{R})$.
$(ii)$ The magnetic field is directly proportional to the number of turns in the coil $(B \propto N)$.
$(iii)$ The magnetic field is directly proportional to the current flowing through the coil $(B \propto I)$.