The correct option is Right-hand thumb rule.
Explanation
When an electric current flows through a straight conductor, it generates a magnetic field around it. The magnetic field lines form concentric circles centered on the conductor. The direction of these field lines depends on the direction of the current flow and is determined by specific directional rules.
Option Analysis
- Right-hand thumb rule Right-hand thumb rule: Correct. Also known as Maxwell’s Corkscrew Rule, this rule states that if you imagine holding a current-carrying straight conductor in your right hand such that the thumb points in the direction of the current, then the direction in which the fingers curl gives the direction of the magnetic field lines.
- Fleming’s left-hand rule Fleming’s left-hand rule: Incorrect. This rule is used to find the direction of the force (motion) experienced by a current-carrying conductor placed in an external magnetic field. It is the principle behind electric motors.
- Lenz’s law Lenz’s law: Incorrect. This law relates to electromagnetic induction. It states that the direction of an induced electromotive force (EMF) or current is such that it opposes the change in magnetic flux that produced it.
- Fleming’s right-hand rule Fleming’s right-hand rule: Incorrect. This rule is used to determine the direction of induced current when a conductor moves inside a magnetic field. It is the principle behind electric generators.
Key Takeaway: The Right-hand thumb rule connects current direction to the magnetic field direction. In contrast, Fleming’s Left-Hand Rule is for force (Motors), and Fleming’s Right-Hand Rule is for induced current (Generators).