Read the following passage and answer the following questions. 

In order to produce a magnetic field, a current is sent through a long, helical coil of wire called a solenoid. Because of the current flowing through each coil, the magnetic field of the solenoid is a superposition of the fields generated by those coils. It is nearly uniform inside the solenoid and close to zero outside, and depending on the direction of current flow, it resembles the field of a bar magnet with a north pole at one end and a south pole at the other. A few variables, such as the current flowing through the coil and the number of turns per unit length, affect the magnetic field generated in the solenoid

A researcher's attempt to observe the variation of the magnetic field with regard to the current in the solenoid yielded the graph below. The magnetic field is measured in milli-Tesla (𝑚𝑇), and the current is expressed in Amperes.