THey are just math conventions. The important thing is voltage can be one of two polarities , and current can flow in one of two directions. In math, we only have positive and negative so we just assign one polarity positive and one negative. To try and make things easier to work with everyone tries to define it the same way. Look at electrons and protons. Scientists weren't sure what direction electrons flowed so the assumed that electricity flowed "this way" and called that positive, so the opposite direction was negative. Well, they guessed wrong. That's why electrons have a negative charge even though it is electrons that are flowing when electricity flows.
So negative current and voltage just mean "the opposite" of whatever way you defined was positive. So if you defined current flowing out of the battery as positive then current flowing into the battery is negative. If you defined the voltage across a resistor as + one way, flowing the other way is negative. THis especially comes up when you are doing circuit analysis and you don't know which polarity the voltage is going to be or what direction the current flows...you just randomly pick one and call it positive, then the other direction is negative. WHen you get the answer, if it is positive then it means it's what you guess. If it's negative it goes the opposite direction or polarity of what you guessed.
Has negative voltage & amps got the same grunt as positive volts & amps??
Grunt? It's all relative- increasing in one polarity is the same as decreasing in the other polarity. ie. if I keep increasing in the negative direction, this is the same as decreasing in the positive direction.
Just say there is a negative going square wave of -10v & -1A going into an inductor, is this the same as charging the inductor with +10v & +1A.?
If so then by increasing the amperage to say -2 amps will this will increase the field strength around the inductor?
Because of the math convention stuff I just talked about. Saying +10 and -10 volts or amps is meaningless without an actual picture to show how you defined the +/- for the inductor. Also, the question in general doesn't make sense for a couple reasons.
1. For ANYTHING, you can't control the voltage AND the current without changing the component itself. Like in a resistor- I can't say I want 10V
and 10A to go through it unless I change the value of the resistor itself.
2. Another reason your example is confusing to read and think about is because you are defining +/- for voltage and current independently. This is directly related to #1 where you cannot control voltage and current independently. You have to define the direction of current relative to voltage or vice versa for things to make sense since they are dependent on each other. Of course, you can do it any way you want as long as it's consistent. But to make it easier for you to communicate your ideas and for other people to understand your ideas, we use a standard:
We use the "passive sign convention" which is:
-Voltage positive/negative is whatever you choose it to be for the component
-If current flows
into the end labelled as
positive(
out the end labelled as
negative) then current is positive
-If current flows
into the end labelled as
negative(
out the end labelled as
positive) then current is positive
This convention causes the following things to happen:
-if current is positive, a component is using current (resistor, a capacitor/inductor charging), if current is negative then the component is supplying current (a battery or an inductor/capacitor releasing energy). I know it's strange that "negative current" means something is supplying power. But instead of thinking negative as decreasing and positive as increasing, think about it in terms of a voltage drop.
-This convention makes it so that if you follows the direction of current flow around a circuit, a resistor will have a
positive voltage drop (the same as a negative rise, but we don't call it that), and batteries will have a
negative voltage drop (same as a positive rise, but we don't call it that either).
-You also have to use some common sense...math does't take into account real life things. FOr example, a resistor NEVER supplies power- just because you guessed the direction wrong doesn't mean it's suddenly supplying power. Resistors consumes power in both directions. Inductors and capacitors on the other hand...in one direction they supply power, in the other direction they consume power (charging). Which way you pick to be +/- is up to you, but if you use the passive sign convention, then + current means it is charging/consuming and - current means it is supplying.