Duration based on effort and capacity

Hi,

I've read a few articles/posts but can't find the confirmation I'n looking for so far. Is it possible to either:

1) Change the % allocation of a resource and have timeline adapt accordingly
For example, if a task has an effort of 8 hours and a work day is 8 hours: if my resource is 
assigned 100% to my project, the task will be completed in 1 day but if my resource is assigned at 
50%, it will be completed in 2 days (I want to be able to put a resource at less than 100% and see the timeline adapt).

or

2) Have duration changed based on effort

I have 1 resource in my project and that resource is assigned to a task: even if I put 100 hours in effort, the duration does not move (it stays at 1 day). I did look into the effort type but it does not help. How can duration updates as effort goes above what is set for a work day? I can put 1 hour work day or 8 hours work day and effort 1 hour or 100 hours, duration stays at 1 day...

Thanks in advance.

Julie