λ1= 769 нм=769*10^-9 м, U1=500 мВ=0,5 В,λ2= 400 нм = 400*10^-9 м,U2= 2 В. h-? hc/λ1=A+eU1,hc/λ2=A+eU2,hc/λ2- hc/λ1=A+eU2-A-eU1,hc(1/λ2-1/λ1)=e(U2-U1),h=e(U2-U1)/(c(1/λ2-1/λ1)),h=1,6*10^-19*1,5/(3*10^8(1/400*10^-9-1/769*10^-9) =2,4*10^-19/(3*10^17(0,0025-0,0013)) = 2,4*10^-19/(0,36*10^15) = 6,67*10^-34 Дж*с.