1. The problem statement, all variables and given/known data An electron is projected from a distance d and with initial velocity u parallel to a uniformly charged flat conducting plate as shown. It strikes the plate after traveling a distance l along the direction of projection. The surface charge density of the conducting plate is equal to Ans :dε0mu2/el 2. Relevant equations 3. The attempt at a solution Electric field of the conducting plate = σ/ε0 Force on the electron in y direction = eσ/ε0 ay = eσ/mε0 l=ut and d=(1/2)ayt2 Solving these ,I get σ = 2dε0mu2/el2 ,but this is incorrect. I would be grateful if somebody could help me with the problem.