In the figure A you have two straight streams of electrons running in the same direction parallel to each other. In the figure B you have two straight wires placed parallel to each other and carrying the current in the same direction. We observe that:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The streams of electrons repell each other whereas the current carrying conductor attract each other
Parallel wires (figure B). Two parallel wires carrying current in the same direction attract each other, because the magnetic field of each exerts an attractive force on the other. The wires are electrically neutral, so there is no electric force to compete with this.
Streams of electrons (figure A). Moving electrons are also parallel currents, so the magnetic force between the two streams is attractive. But the electrons also carry charge, so the streams exert a Coulomb repulsion on each other. For speeds far below the speed of light the electric repulsion is much larger than the magnetic attraction, so the net force is repulsive.
\( \displaystyle \frac{F_{\mathrm{magnetic}}}{F_{\mathrm{electric}}} = \frac{v^{2}}{c^{2}} \ll 1 \)
So the streams repel and the wires attract.