Magnetic Resonance Imaging (MRI) is a widely used diagnostic technique. It shows internal organs in minute detail. This technique is based on Nuclear Magnetic Resonance (NMR). Our tissues mostly contain water and about two thirds of the atoms in human body are 'hydrogen'. Nucleus of a hydrogen atom is a proton. Proton, like electron, has a spin angular momentum and also a magnetic moment. Thus proton can be regarded as a tiny magnet. Its spin magnetic moment is nearly $2.79{\mathrm{\mu }}_{\mathrm{n}},\text{ where }{\mathrm{\mu }}_{\mathrm{n}}=\frac{\text{ eh }}{4{\mathrm{\pi m}}_{\mathrm{P}}}=5.05\times {10}^{-27}\mathrm{J}/\mathrm{T}$ is called a nuclear magneton; here m_p is the mass of proton. Let us apply an external magnetic field $\overrightarrow{\mathrm{B}}$ and discuss how proton behaves. Obviously, proton will behave in a manner similar to a magnet placed in an external magnetic field. We know that potential energy of a magnet of magnetic moment $\overrightarrow{\mathrm{\mu }}$ when placed in an external magnetic field $\overrightarrow{\mathrm{B}}$ can be expressed as $\mathrm{U}=\mathrm{\mu {\rm B}}(1-\mathrm{cos\theta }),$ where $\mathrm{\theta }$ is the angle between $\overrightarrow{\mathrm{\mu }} \mathrm{and} \overrightarrow{\mathrm{B}}$. Due to the interaction of external magnetic field and the spin magnetic moment of proton, energy of the proton becomes quantised resulting in two allowed 
state-(l) spin of the proton aligned with the magnetic field-(2) spin of the proton antialigned i.e., opposite to field. These states will have different energy. In fact, the energy difference between the two states is very small and photons whose energy matches the energy gap can cause transitions of protons between the two energy states. These transitions are called spin-flip transitions. A set-up for conducting such experiment is shown in figure. A coil is wrapped around the sample and alternating current of variable frequency is made to pass in the coil. Protons in the sample absorb power from the coil when frequency of current in the coil is the same as required to induce transitions between the two energy states of protons. This is called Resonance absorption of energy and the technique called 'Nuclear Magnetic Resonance'. With B = 1.5 T and, as mentioned above, spin magnetic moment of proton ${\text{=2.79\hspace{0.17em}μ}}_{\mathrm{n}},\mathrm{\hspace{0.17em}\hspace{0.17em}}({\mathrm{\mu }}_{\mathrm{n}}=5.05\times {10}^{-27}\mathrm{J}\mathrm{/}\mathrm{T}),$ answer the following questions.