Which rule helps to determine the direction of force acting on a current-carrying conductor in a magnetic field?

The correct option is Fleming's left-hand rule.

Understanding the Concept:
When a current-carrying conductor is placed in an external magnetic field, it experiences a mechanical force due to the interaction between the magnetic field produced by the current and the external magnetic field. The direction of this magnetic force can be easily determined using Fleming's left-hand rule.

Fleming's Left-Hand Rule Statement:
Stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other:

1. The Forefinger points in the direction of the magnetic Field.
2. The Middle finger points in the direction of the electric Current.
3. The Thumb points in the direction of the motion or the magnetic Force acting on the conductor.

Explanation of Other Options:
- Ampere's rule (or Right-Hand Thumb Rule): Used to determine the direction of the magnetic field generated around a current-carrying conductor.
- Faraday's law: Describes the phenomenon of electromagnetic induction and states how a changing magnetic field induces an electromotive force (EMF) in a circuit.
- Right-hand rule (Fleming's right-hand rule): Used to determine the direction of induced current when a conductor moves in a magnetic field.

Therefore, Fleming's left-hand rule is the rule used to find the direction of force acting on a current-carrying conductor placed in a magnetic field.