A magnetic needle in a uniform fieldएकसमान क्षेत्र में चुंबकीय सुईA magnetic needle in a uniform field

NCERT Fig 5.3(b) · Class 12 Physics · Chapter 5 · interactive diagram

Parts and what they mean

• Uniform magnetic field B (एकसमान चुंबकीय क्षेत्र B) — Same magnitude and direction everywhere, so the force on the N end and the S end cancel: net force zero.
• Compass needle (कम्पास सुई) — A small magnet free to turn about its centre (red = N end).
• Magnetic moment m (चुंबकीय आघूर्ण m) — Points from the S end to the N end of the needle; unit A m² (= J T⁻¹).
• Angle θ between m and B (m और B के बीच कोण θ) — θ = 0: m along B (stable). θ = 180°: m opposite to B (unstable).
• Restoring torque (प्रत्यानयन बल आघूर्ण) — τ = mB sin θ. Here m × B points into the page, so the needle turns clockwise — towards B.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 5.3(b). Report a mistake