A circuit is a __closed __loop that electrons travel through. If a circuit is open, that means that the wires are cut off or there is a gap so that electrons cannot make a full trip around the circuit. If a circuit is closed, there is a complete path that electrons can take.

DC Circuits stand for a **D**irect **C**urrent (DC) circuit. This is opposed to an **A**lternating **C**urrent (AC) circuit which is not covered in AP Physics 1 as it is much more complicated.

Current (I) - How much charge passes through an area over time. Measured in amperes (A).

Resistance (R) - How much an object resists current flow. Measured in ohms ( Ω ).

Voltage (V) (potential difference) - the difference in potential energy between two locations. This is sometimes referred to as potential difference. Measured in volts (V).

DC circuits in real life often look like a tangled ball of yarn. In order to have a clearer visualization of circuits in physics, we use DC circuit graphs as a simpler representation of a circuit.

A battery moves electrons from a low potential state to a high potential state.

A resistor resists current. Lightbulbs and motors can also be treated as resistors because they convert electrical energy to light or kinetic energy and therefore resist the current.

A switch switches the current. It turns something on and off by opening and closing the circuit.

An ohmmeter measures the resistance of a resistor (ohms -> ohmmeter)

An ammeter measures the current (amperes -> ammeter)

A voltmeter measures the voltage (volts -> voltmeter)

**V = IR:** Voltage is Current times Resistance.

I = V/R

R = V/I

**P = IV:** Power is Current times Voltage. Remember **P**oison **IV**y!

__Voltage__

Calculating voltage can be thought of as adding the voltages to get form point A to point B.

Series circuit voltage: Vtotal = V1 + V2 + V3 + V4...

Total voltage is the sum of all voltage drops in series.

Parallel circuit voltage: Vtotal = V1 = V2 = V3 = V4

Total voltage is the same as just one of the voltage drops. All voltage drops are equal.

__Current__

Series circuit curren: Vtotal = V1 + V2 + V3 + V4...

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