1. (1) the potential difference of the power supplies (2) the nature of the pathway through the loads are the two things of the amount of current flow in a circuit and the energy transferred to useful device.
2. Two of the simple circuit, the first circuit allows the circuit to pass though the load easier than the second circuit, in the two circuits, their potential difference is the same, but the pathways are different.
3. The more difficult the pass, means the more opposition there is to flow. Electrical resistance is the measure of this opposition to flow.
4. R is the resistance in volts/ampere, Ohm（Ω）is the unit of the resistance.
5. V/I this ratio is called Ohm’s law
6. The resistance of a conductor depends on 4 major things: its length, cross-sectional area, material, and its temperature.
7. Series circuit and parallel circuit are the two simplest ways to connect conductor and loads.
8. In a series circuit the loads are connected one after another in a single path
9. In a parallel circuit the loads are connected side by side
10. Kirchhoff’s current law: the total amount of current goes into a junction point equals the same amount of current that flows out of that same junction.
11. Kirchhoff’s voltage law: the total amount of potential decreases in any complete circuit loop is the same number as the electrical potential increases in that circuit loop
12 . Vt = V1+V2+V3 so, there is no gain or loss of electric charge or energy in a circuit.
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