An electron beam moving with uniform velocity is gradually diverging. When it is accelerated to a very high velocity, it again starts converging. Why?

Explanation

Moving electrons, apar from electrical repulsion experience magnetic attraction also. If the electron beam is moving under normal conditions, the electrical repulsive force is much stronger than the magnetic attraction and hence the beam diverges. When the electron beam is moving at very high velocity, the magnetic force of attraction becomes more effective than electrical repulsion and the beam starts converging.