is a glow in the dark rubber ball a light source?
Yes, it is. Otherwise you would not see it. It stores light it has been subjected to previously.
your textbook may have made a semantic distinction amongst different things that emit light (and if so, use the textbook's rules!), but i'd say that if something is emitting photons (even if temporarily) then it's a light source - so YES! OTOH, the glow-in-the-dark-ball is just remitting some fraction of the light it absorbed some minutes ago. in that sense, i can see how your teacher might put such a ball in the category of *not* a pure source, but just a reemitter... then again, light bulbs convert electrical energy into light (and are a light source i think) and your rubber ball is reemitting absorbed light. so, i can see it both ways actually. check w/ your textbook... off the cuff though, i'd say Yes. it emits light, so it's a light source. cheers
