Part A Magnetic field lines form closed loops Magnetic field lines form closed loops Around and through bar magnets. Through current-carrying loops. Around current-carrying straight wires. All of the above.

Magnetic field lines form closed loops around current carrying straight wires.

Explanation:

Magnetic field lines is known to form closed loop (which also serves as a bar magnet) around current carrying conductor in a magnetic field. This direction of the loop around the conductor either clockwise or anticlockwise will determine the direction of current in the conductor.

This directions can be determined using the Maxwell cockscrew or clenched fist rule.

According to clenched fist rule which states if the conductor is grasp with the right hand, the curled finger will point in the direction of the magnetic field and the thumb will point in the direction of the current.

Note that the magnetic field lines around the conductor also behaves like a bar magnet.

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