I don't think there is a set weight for beginners, because each person is at a different level when they begin. So instead, focus on the repetitions and guide yourself off that. For example, try going for at least 8 repetitions, I usually do different repetitions for different work-outs, but for arms I go with 12.
So, if you are trying to get 12 repetitions in, then test out a light weight and do 12 repetitions, if you think you can lift heavier, then try a heavier weight. Once you are lifting a certain weight that you cannot exercise 12 repetitions with, then stop there and use that weight until you can. And gradually move from there.
-Roek