Final answer:
The magnetic field lines around a straight, current-carrying wire form circles around the wire, which can be determined using the right-hand rule. option a is correct
Step-by-step explanation:
option a is correct The magnetic field lines due to a straight, current-carrying wire are circles around the wire. This is because the magnetic field created by an electric current in a long straight wire manifests as concentric circles centered on the wire. Importantly, these magnetic field lines are tangent to the concentric circles at any point and have no component pointing towards the wire. The direction of the magnetic field can be determined using the right-hand rule, which in this context means that if you hold the wire with your right hand so that your thumb points in the direction of the current, your fingers will curl in the direction of the magnetic field (B).
In experiments, this circular pattern can be visualized with the aid of small compass needles or iron filings placed near the wire. When a current is flowing through the wire, the compass needles will align tangent to the circles, and iron filings will form circular patterns that illustrate the magnetic field lines. As the distance from the wire increases, the magnetic field strength decreases, which is represented by the increased spacing between the field lines.