The correct option is A is false but R is true
Explanation
The force experienced by a current-carrying conductor placed in a uniform magnetic field is governed by the interaction between the magnetic field produced by the current and the external magnetic field. The magnitude of this force is determined by the angle between the direction of the current and the magnetic field vector.
Statement-wise Analysis:
- Assertion (A): Incorrect. The magnitude of the force ($F$) acting on a current-carrying conductor of length $L$ carrying current $I$ in a magnetic field $B$ is given by the formula:
$F = B I L \sin\theta$
Here, $\theta$ is the angle between the direction of the current and the magnetic field. When the conductor is placed parallel to the magnetic field, $\theta = 0^\circ$ or $180^\circ$. Since $\sin(0^\circ) = 0$, the force experienced is zero (minimum), not maximum. The force is maximum when the conductor is placed perpendicular ($\theta = 90^\circ$) to the field. - Reason (R): Correct. Fleming's Left-Hand Rule is the standard rule used to determine the direction of the force (or motion) acting on a 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, the forefinger represents the magnetic field, the middle finger represents the current, and the thumb points in the direction of the force.
Key Takeaway: A current-carrying conductor experiences zero force when aligned parallel to a magnetic field and maximum force when aligned perpendicular to it. The direction of this force is determined by Fleming's Left-Hand Rule.