Question

I am currently doing an experiment on continous wave NMR and was wondering if someon could explain the theroy behind how resonace is created in a sample, for example hydrogen 1.

If possible type would be best as I have trouble reading, on my laptop the hand written answers somtimes.

Answer 1

To understand resonance, it would be helpful to recall the forced oscillations from classical physics, where we learnt that the resonance occurs when the frequency of the applied force is close to one of the natural frequencies of vibration of the driven system. Similarly, when we are considering quantum systems like hydrogen where electronic spin in the presence of magnetic field (constant) has discrete energy levels. That means that the system will make transtion from one energy level to another energy levels when a certain energy is supplied (). Next, in the presence of magnetic field the electronic spin precess (frequency is called Larmor frequency E = ), which is similar to the precession of a top due to earth's gravitational force in some sense. Now if we use an external magnetic field with the same frequency as the Larmor frequency which is natural frequency of the system or sample, then a resonance will occur, which is similar to the resonance occuring for an oscillator when a force with same frequency as natural frequency of the oscillator is applied.