1. E (with dielectric) = E (w/o dielectric) – Ei =E/k what is E then? Original Electric field? But I thought the original one was E without dielectric? Do these two both refer to the same electric field? 2. Whether it's "First the wave theory" or any questions relating to wave in high school course, the question always says: assuming monochromatic light. So why every time it’s monochromatic? what if it's not? what will happen? 3. m* NA=M, NA is Avogadro’s constant. I am always confused with this formula. Which is bigger in this formula, little m or big M?