For a step potential function, assume that the potential barrier at x = 0 is three times as large as the total energy of an incident electron, whose velocity is 1 km/s at x < 0. The mass of electron is 9×10-31 kg. (a). calculate the penetration depth d of the electron impinging on the potential barrier. (b). calculate the probability of finding the electron at a distance of (l=10nm) into the potential barrier.