Do magnetic forces obey Newton’s third law. Verify for two current elements dl₁= dl i located at the origin and dl₂ = dl j located at(0, R, 0). Both carry current I.

<p>This is a Short Answer Type Questions as classified in NCERT Exemplar</p><p><strong>Explanation-&nbsp;</strong>In Biot-Savart’s law, magnetic field B is parallel (II) to id × r and idl have its direction along the direction of flow of current.</p><p>Here, for the direction of magnetic field, At dl2, located at (0, R,0) due to wire d1 is given by B I | dl × r or I ×j (because point (0, R,0)lies on y-axis), but I × j= k</p><p>So, the direction of magnetic field at d2 is along z-direction.</p><p>The direction of magnetic force exerted at d2 because of the first wire along the x-axis</p><p>F =i (l&nbsp;<math><mo>×</mo></math>&nbsp;B) i.e., F| (i&nbsp;<math><mo>×</mo><mi>k</mi></math>&nbsp;) or along− j direction.</p><p>Therefore, force due to dl1 on dl2 is non-zero.</p><p>Now, for the direction of magnetic field, At d1, located at (0,0,0) due to wire d2 is given by</p><p>B I | dl × r or j ×−j (because origin lies on y-direction w.r.t. point (0, R,0).), but j ×−j =0.</p><p>So, the magnetic field at d1 does not exist.</p><p>Force due to dl2 on dl1 is zero.</p><p>So, magnetic forces do not obey Newton's third law.</p>

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