How do you know if a microscope lens is scratched damaged or has debris on it?

Well i got this microscope from the goodwill, and it has no slides and the light on it dont work so i use my lamps bare lightbulb to lighten the microscope. and i see stuff with a bare lens but idk if its scratches debris or what? its like some dark black lines and stuff. i see small clear things that look like theyre swimming around. i think my microscope is 50MM by 500MM zoom. any tips or anything?i also used a Q-tip with alcohol on it to clean the lenses. it dident helo.