there is no need to count the hours. it is upto your potential that how many hours you can spend
In general, to obtain a Ph.D. you have to put in time similar to a full-time job, perhaps even more so, if you want to finish in a reasonable amount of time.
This is true. Generally on a Ph.D. track (in the sciences, engineering, math and even other degree programs) you are paid a stipend and receive tuition waivers... think of this monetary benefit as a salary that you get for working full-time on your research and teaching obligations... and if you think the monetary compensation is low, also remember that it's helping you along the path to a credential (your degree) and giving you valuable experience.
Most PhD demand a huge amount of commitment.
I would guess anywhere between 40 and 80 hrs a week.
Personally, I found it hard to work 40 hours a week on my PhD, depending on what you count as "work". For example, does teaching count as work? or reading about only very obliquely related topics for fun? or preparing to give a seminar that really isn't necessary for your project? or drifting off to think about my project while I'm supposed to be listening to someone in conversation? or messing around with a dubious possibility when I'm trying to solve some problem?
I have tried to keep track and force myself to work "full-time" hours, but this invariably left me feeling really exhausted and didn't help much. I was generally pretty happy if I did four hours per day of work on my actual project, and that was if I was working conscientiously. I found the quality of work is better when you're not counting the time go by.
Also, I find when I'm learning something new, I have really low stamina. Once I've got the hang of something, I can work for hours and hours.
It might depend on which country you are doing your PhD in though. When people talk about working really long hours I always wonder what they were doing.
I would consider everything that encompasses your position as a graduate student in the university.
That includes: taking classes, teaching, tutoring, reading, homework, research, preparing for seminars, talking to professors and attending colloquiums.
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