# Answer to Question #31954 in Electromagnetism for Samantha

Question #31954

Discuss how positive and negative charges go from being stored to active.

Expert's answer

First, there is one real particle in this matter-based world which moves to carry electricity, and it is the electron, which is negatively charged. (We won't expand this at this time to cover electrochemistry.)

In semiconductors, there is also this entity called a 'hole', which acts like a particle, but it isn't really. 'Holes' are positively charged.

When you analyze circuits (i.e. applying Kirchoff's Laws, etc.), current flows from positive to negative. Current is defined as charge per time. If the current is in a wire (in which case it is electrons) or within a semiconductor (in this case there can be positive or negative carriers) it is still charge per unit time.

Charge has a positive or negative sign. If you have some means to count charge carriers passing through an imaginary cross section in your circuit, you can measure current--you have to multiply by the charge per carrier.

You can store charge (i.e. capacitor). You can't store current. In a semiconductor device, you can have positive and negative charges that flow toward each other, but if you look at the current at any cross section through a 2-terminal device, the current is the same.

There are methods for assigning +'s and -'s to pins of elements in electric circuits, and for assigning +'s and -'s to currents. Yes, you could say that the flow is irrelevant to some degree. The methods are there in order to make the creation of equations that describe the circuit for analysis easier, and to ensure that the equations are self-consistent.

In semiconductors, there is also this entity called a 'hole', which acts like a particle, but it isn't really. 'Holes' are positively charged.

When you analyze circuits (i.e. applying Kirchoff's Laws, etc.), current flows from positive to negative. Current is defined as charge per time. If the current is in a wire (in which case it is electrons) or within a semiconductor (in this case there can be positive or negative carriers) it is still charge per unit time.

Charge has a positive or negative sign. If you have some means to count charge carriers passing through an imaginary cross section in your circuit, you can measure current--you have to multiply by the charge per carrier.

You can store charge (i.e. capacitor). You can't store current. In a semiconductor device, you can have positive and negative charges that flow toward each other, but if you look at the current at any cross section through a 2-terminal device, the current is the same.

There are methods for assigning +'s and -'s to pins of elements in electric circuits, and for assigning +'s and -'s to currents. Yes, you could say that the flow is irrelevant to some degree. The methods are there in order to make the creation of equations that describe the circuit for analysis easier, and to ensure that the equations are self-consistent.

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