The rule to determine the direction of a force experienced by a straight current carrying conductor placed in a magnetic field which is perpendicular to it is

Fleming's left-hand rule is used to determine the direction of the force experienced by a straight current-carrying conductor placed in a magnetic field.

According to this rule, if the thumb, forefinger, and middle finger of the left hand are stretched mutually perpendicular to each other, such that the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the current, then the thumb gives the direction of the force experienced by the conductor.

The right-hand thumb rule is used to find the direction of the magnetic field around a current-carrying wire.

Fleming's right-hand rule is used to determine the direction of induced current.

Hund's rule is a principle of atomic chemistry related to the filling of electrons in orbitals.

Answer: Fleming's left-hand rule