Shown in the given diagrams (a), (b) and (c) are the magnetic fields around different systems. Identify them. Compare the pattern of the field lines in all the three systems.

a.

In this setup, the magnetic field around a current carrying solenoid is shown. The field lines inside a solenoid are in the form of parallel straight lines. It indicates that the magnetic field is uniform inside the solenoid. One end of solenoid behaves as North pole and the other as South pole.
b.

The magnetic field lines are circular around a current carrying wire. These concentric circles become larger as we move away from the wire indicating decrease in the decrease in magnetic field strength with increase in the distance.
c.

The magnetic field due to current carrying loop is shown here. The magnetic field due to a current carrying straight wire is inversely proportional to the distance from it. They form concentric circles around the wire having increase in radius with distance. Similarly, at every point of the loop, the concentric circles would become larger as we move away from the wire. At the centre of loop, the arcs of these big circles appear as straight lines.