Both seem to be question particles. What's the difference between them (in meaning & usage)?
They are different in tone side, for example when you ask some one if have dinner, you can use 你吃晚饭了吗? or 你吃晚饭了么? Both are OK, because it's not strong sense of doubt, just ask, not a question style.
But you can not use 么 in 你拿得出证据证明他的清白吗? In the sentence "你拿得出证据证明他的清白吗?" has a style of you have to give me the answer, and mostly you can not.
So, mostly, you can use 吗 and 么,but with the strong tone, especially rhetorical question you can just use 吗.
么(ma)同"吗"
That is saying 么(ma) is equal to 吗(mǎ).
If you said the simple usage of 么(mē) and 吗, there is some difference.
么 usually explain the not strong sense of doubt, and 吗 is little stronger. But the level of doubt sense is often depended on volume, if you speak loud , 么 can be stronger than 吗 in some condition.
And more, there are some other different usages, for example , people say 干什么 rather than 干什吗, and there is network language 干神马 which has the same meaning of 干什么.
ma.. – Wang Dingwei Jan 6 '15 at 5:26