Question

Two streams of electrons are moving parallel to each other in the same direction. They_____

• A. attract each other
• B. repel each other
• C. cancel the electric field of each other
• D. cancel the magnetic field of each other

Answer 1

The correct option is B repel each other

If the beams were stationary, they'd repel (because negative charges repel). Once the beams are moving we get the magnetic effects in addition, which reduces the repulsion. The magnetic attraction only becomes strong enough to cancel the electric repulsion at c. Therefore the streams will repel each other due to electric repulsion.