The correct option is Right-hand thumb rule.
Explanation
A current-carrying conductor generates a magnetic field around it. For a straight conductor, the magnetic field lines form concentric circles centered on the wire. The direction of these field lines depends on the direction of the current flow and is determined by specific mnemonic rules.
Detailed Analysis:
- Right-hand thumb rule (Correct): This rule is specifically used to find the direction of magnetic field lines around a straight current-carrying conductor. It states that if you imagine holding the conductor in your right hand with the thumb pointing in the direction of the current, the direction in which your fingers curl represents the direction of the magnetic field lines.
- Fleming’s left-hand rule (Incorrect): This rule is used to determine the direction of the force (or motion) experienced by a current-carrying conductor placed in an external magnetic field (principle of electric motors).
- Fleming’s right-hand rule (Incorrect): This rule is used to determine the direction of induced current in a conductor moving within a magnetic field (principle of electric generators).
- Lenz’s law (Incorrect): This law relates to electromagnetic induction, stating that the direction of the induced electromotive force (EMF) or current is such that it opposes the change in magnetic flux that produced it.
Key Takeaway:
The Right-hand thumb rule relates current direction to magnetic field direction. In contrast, Fleming's rules relate magnetic field, current, and force/motion (Left for Motors, Right for Generators).