3 Things Necessary to Get Current to Flow

General Notes: 3 things necessary to get current to flow:  Something to push the charge along (a voltage = potential difference, usually a battery or a generator)  Conductors (wires or some sort of bars in which the charges can “flow”)  A closed loop (an electric circuit requires literally a circle, starting at the positive, high potential energy terminal of the battery and moving towards the negative, low PE terminal of the battery)

Ohm’s Law: Relates voltage, current, resistance of an electric circuit V = IR (voltage) = (current) x (resistance)

Power: All circuits dissipate or use up power. Remember from first semester that Power=Energy/time. So power is directly related to the amount of energy used in a circuit. P = IV

Equivalent resistance: All circuits, no matter how complex, can be broken down to be represented as a single voltage source and a single resistance. The method for calculating this “equivalent resistance” varies depending on the type of circuit (see rules below).

Series Circuits:  Only one path for charges to follow therefore current is the same everywhere in the circuit

 Req = RA + RB + RC … ad infinitum due to only one path for electrons to flow.  Series circuits are voltage dividers. This means that the amount of voltage or “push” used up as current flows around the loop changes across each different resistor The voltage drops across all the resistors in the circuit as you go around the entire loop need to add up to the voltage of the battery or other power source driving the circuit. Vbatt = VA + VB + VC …etc

Parallel Circuits:  Multiple paths for current to follow. At any node (intersection) in the circuit the current flowing into the node must equal the current flowing out. Analogy: think of the wires like pipes carrying water.

 1/ Req = 1/RA + 1/RB + 1/RC … ad infinitum Be careful! You don’t want to solve for -1 1/Req, you want Req so you must take the inverse (use the x key on your calculator) of the sum of the fractions.  Voltage drop across each branch of the circuit is the same as the voltage of the battery. Notice that each branch of the circuit is connected in its own separate loop, directly to the battery. Vbatt = VA = VB = VC …etc