Hi Rio, I would suggest for the second sentence you say "Please let me know as soon as you've finished the work." If you say to someone "Please let me know when you've finished the work" you are asking the person to let you know when they are finished the work but you have not indicated when they should let you know. If you say to someone "Please let me know as soon as you've finished the work", you are asking the person to let you know when they are finished, but it is indicating that you would like to know this right away. So when they finish the work, they should let you know immediately.

Yes, there is a big difference! In sentence a) it gives the impression that the person hasn't finished their work whilst in sentence b) it gives the impression that they have already finished their work. (and the person speaking to them is asking for verification to an earlier question) Hope this helps ;)

Thank you so much for your help, Lori! You helped me out. :)

Hi Ryo, It would not be grammatically correct to say "Please let me know as you've finished the work." If you want someone to tell you when they have finished the work, then sentence a is good for that, and if you would like someone to tell you right after they have finished the work then you could say "Please let me know as soon as you've finished the work."