Need help understanding appliance ratings I keep coming across things like "A filament lamp rated 12 V, 1.0 A", or "a heating element rated 230V, 500W".
I think the first one is saying that a 12V potential difference across it will make a current of 1A flow through it.
Can someone please explain in detail what these (and other similar ones) mean?
Thanks!
 A: A rating of 

A filament lamp rated 12 V, 1.0 A

means that it is designed to work at a voltage of 12V, and at this voltage, it consumes 1A current. 

a heating element rated 230V, 500W

is intended similarly. It means that the element is designed to work at 230V, at which it consumes 500 W power. 
These sort of specifications made no sense to me when I was a kid knowing a little bit of Physics - "Why don't the specify the resistance directly and let us do the maths"! But it makes sense, not all elements have fixed resistances, it is generally a non-linear I-V curve and at some designated voltage, at which the device is intended to work, they tell you the useful parameter. Please notice that e.g. a lamp filament doesn't have a constant resistance, and the argument generalizes. 
So, in general, these specifications have the form - [(parameter value at which it is designed to work), (some useful parameter value, current or power, consumed when the device works at the value designated at parameter 1)].  
