An electron entering an extended stationary and uniform electric field at a velocity βc penetrates into this field to a depth l. The electron velocity is directed along the field. To what depth will the electrons penetrate, if, on the contrary, an electric field hits the stationary electrons with the same speed? Solve this problem in two ways, using: a) the effect of relativistic distance reduction, b) the relationship between the work of A and the change in the particle mass ∆m : A = c²∆m.