microphones in webcams

If i get a webcam with a mic built in will the mic still work even if the cam isn't being used.For instance,on yahoo messenger if i am not on a video call(only voice call) will the mic be operating so i can use voice call or must I keep my other mic plugged in?Or if I am using recording software to record myself playing piano will the webcam mic be functioning even thought i don't have the cam turned on.Will I have to plug in my normal mic.I hope you see what I am trying to ask.Thank you.

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