A long solenoid with diameter 4 cm is in a vacuum, and a lithium nucleus ( 4 neutrons and 3 protons ) is in a clockwise circular orbit inside the solenoid ( Figure 20.102 ). It takes $\mathbf{50}\mathbf{ns} \left(\mathbf{50}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{9}}\mathbf{s}\right)$ for the lithium nucleus to complete one orbit.

(a.) Does the current in the solenoid run clockwise or counter clockwise ? Explain including physics diagrams.

This is the figure of a long solenoid having a diameter$4cm$ , where lithium nucleus is revolving inside the orbit in clockwise direction.

Also, the interval of time required to complete one oscillation is$t=50\times {10}^{-9}s$

The solenoid contains a lithium nucleus which is circling clockwise. So there exist a centripetal force inside the solenoid acting towards the orbit, which helps in rotate the lithium nucleus in clockwise. The magnetic field acting on the lithium nucleus is out of the page because the velocity of the lithium is upwards and force is acting on right side.

The counter clock wise current inside the solenoid produce a magnetic field which acts outward. If thumb is taken as the magnetic field the fingers are the direction of current flows.