Hello friends, I am a student of VLSI and have initial topics of quantum mechanics in my course work. I am experiencing some difficulties in understanding the same and i will post my queries here. Some of my doubts may be silly (as i am going through these topics after 6 years), hence i request for your patience. To start with, i am quoting a statement by de broglie (Query 1) I am experiencing trouble understanding the bold parts. Please explain it.