Elemental, im currently M.Sc in physics myself, and noticed that weed had this same effect in me.
Fortunately i only started to smoke in the last year of graduation, so it was not affected by my smoking.
But my M.Sc surely was. I noticed while i was high, i could understand things better than when i was sober, mainly abstract things, theories, and such. But when the high did wear off and i was burnt out, i had to struggle to make even the simplest calculations.
So, my own advice would be to smoke when you needed to understand abstract/theoretical things, like at the classes, but do the "hard work" (calculations, etc) while sober, the most sober you could get.
Also, smoking can provide INCREDIBLE insights... i had a lot of ingenious ideas while high... and surely im not the only one... there was great physicists who used to smoke... we all know Einstein used to smoke a pipe... and while no biography states everything he used to smoke in it, i like to think he used to enjoy some good weed... :rastasmoke::jointsmile::thumbsup: