Science — CBSE Class 10 board question

(i) When current flows from X to Y (upward), the magnetic field lines form concentric circles around the conductor. The direction of circles is anticlockwise when viewed from above (i.e., from Y end), as determined by the right-hand thumb rule.
(Student should draw concentric circles around conductor XY with anticlockwise arrows when current goes X→Y upward.)

(ii) The rule used is the Right-Hand Thumb Rule.
Statement: Imagine holding the current-carrying conductor in your right hand such that the thumb points in the direction of current. Then the fingers wrap around the conductor in the direction of the magnetic field lines.

(iii) Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other. 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.

Direction of force on the electron: Since electrons move opposite to conventional current direction, applying Fleming's left-hand rule (reversing current direction), the force on the electron is directed into the page.

Source: Chapter 12, Sections 12.2.2 and 12.3

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• (i) The key point is concentric circles — examiners expect this term plus arrows showing correct direction (anticlockwise for upward current when viewed from top).
• (ii) Name the rule first, then state it exactly as in the textbook. Both are needed for the 1 mark.
• (iii) Two things are tested: the statement of Fleming's Left-Hand Rule (forefinger = field, middle finger = current, thumb = force/motion) AND applying it correctly to an electron. The crucial trick: current direction is opposite to electron motion, so reverse the conventional current before applying the rule. The standard textbook answer (Example 12.2) gives "into the page" — match the diagram given.