I'm trying to understand the difference between amperes and watts. I have a string of LEDs that say require 5W of power and 5amps. What's a good way to memorize the difference and significance of these two values?
Electronic – can somebody give an analogy of what an ampere is
electromagnetism
Related Solutions
There is a configuration of two coils, known as a Helmholtz coil, that is supposed to produce a nearly uniform field. The idea is to have two coils that are separated by a distance about the same as the diameter of the individual coils. Going with this, the coil diameter would obviously have to be about the same as the length of your rails, so would be rather large relative to the rest of the apparatus.
But you might not need an exactly uniform field anyway. If you had a field that was non-uniform, but symmetric across a plane that divides the mid-line of your rails, the forces on the movable bar should be in-line. It might be possible to produce a field like that by using two rectangular coils, same width as the rail separation, with one half above the plane of the rails and the other below.
We usually draw the inductor symbol as a coil of wire which can be very misleading. You have to take a look at the B-field around a straight wire then all the sudden your analogy makes perfect sense.
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Best Answer
Well, the definition of an ampere is quite figurative: It is the current through two parallel infinitely long and thin wires, that are 1 metre apart from each other, so that the force between them is exactly \$2 \cdot 10^{-7}\$ Newton per metre (thanks to @rioraxe for checking the numbers).
Admittedly, this is not easy to transfer to reality. In fact, it is very hard to give another example. It is easier, when you think in power, rather than current. At 5 V, you get 5 Watts. At 230 V you get 230 W at 1 A.
Concerning your case with LEDs at 5V, you need to take light efficiency into account. LEDs have around 80 to 120 Lumens per Watt. So if you have 25 watts in LEDs, you can think of around 2500 Lumens, which is around as much as two Lightbulbs with 100 Watts have.