DC Circuits

Current and Resistance

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 Direct Current (DC) circuit. This is opposed to an Alternating Current (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).

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DC Circuit Graphs

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.

Parts of a graph

Battery

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

Resistor

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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.

Switch

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

Ohmmeter

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

Ammeter

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An ammeter measures the current (amperes -> ammeter)

Voltmeter

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A voltmeter measures the voltage (volts -> voltmeter)

Important Equations

Formula Sheet + Explanations

V = IR: Voltage is Current times Resistance. 

I = V/R

R = V/I


P = IV: Power is Current times Voltage. Remember Poison IVy!


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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