The magnetic field inside a long straight solenoid-carrying current

The magnetic field lines inside a long straight solenoid carrying current are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid.

The magnitude of the magnetic field inside an ideal long solenoid is given by $B = \mu_0 n I$, where $n$ is the number of turns per unit length and $I$ is the current. Since $\mu_0$, $n$, and $I$ are constant, the magnetic field is uniform inside the solenoid.