Science — CBSE Class 10 board question

(i) Fleming's Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb points in the direction of force on the conductor.

(ii) Since an alpha particle is positively charged and an electron is negatively charged, the direction of conventional current for an electron is opposite to that of an alpha particle. Therefore, the electron will be projected towards the south.

Source: Chapter 12, Section 12.3 — Force on a Current-Carrying Conductor in a Magnetic Field

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• For (i), examiners expect the name Fleming's Left-Hand Rule plus a clear statement of all three fingers and what each represents. Missing the name loses a mark.
• For (ii), recall that conventional current direction is opposite to electron motion. An alpha particle (positive charge) moving north gives conventional current northward; an electron moving in the same magnetic field has opposite conventional current, so the force reverses — projecting it south. Use Fleming's Left-Hand Rule mentally to verify.