PHP Code to Check if Radio Button Selected

Hi everyone Just a small issue. I have a form with a radio button (urgent), with two choices yes and no. If yes a text box is to be validated. I have the validation already setup and working (JS). But need to setup a JS/php IF statement to check if the radio button urgent and if Yes to allow the text box validation otherwise ignore it. At the moment it is validating on everything (ie urgent or not). So just need a short JS or php script to check state of the radio button. Will then put the validation inside the if urgent section. Hope that is clear. You will need to setup a test document to show me. I know should be easy but spent a few minutes on it and just can’t quite get it. Ta.