“Did you wash your hands?” or “Have you washed your hands?” and why? [duplicate]

Question

Possible Duplicate:
How do the tenses in English correspond temporally to one another?
When do I use present perfect tense instead of the simple past?
When will “Present Perfect vs. Past Tense” cases be affected by culture?
“Did you find” versus “have you found”

The first sentence hasn't specified time, but I have seen it.

Answer 1

The perfect tense, used in the second sentence, indicates something done in the past, which has a continuing effect on the present. To ask the first could mean nothing, as their hands could have been washed yesterday, or maybe even today and are now dirty. The second, however, is much more effective in interrogation.