(a(i))[2]
State and explain why the large constant magnetic field is required.
(a(ii))[3]
State and explain why the magnetic field is non-uniform.
(b)[2]
In magnetic resonance imaging, the de-excitation energy $E$ (measured in joule) of a proton is defined by $E = 2.82 \times 10^{-26} B$, where $B$ is the magnetic flux density measured in tesla. This energy is released as a photon of electromagnetic radiation in the radio-frequency range. Calculate the magnetic flux density needed for the radio frequency to be $42\,\text{MHz}$.