AP®︎/College Physics 1
DC Circuit and electrical power review
Review the components of a circuit and their symbols such as battery, resistor, and switch. Analyze how the power of a resistor is related to the current and electric potential difference across the resistor.
|Equation||Symbols||Meaning in words|
|is power, is current, and is electric potential difference||The rate at which energy is transferred from a resistor is equal to the product of the electric potential difference across the resistor and the current through the resistor. Scalar quantity with units of Watts ().|
Circuit component definitions and symbols
Resistors are electrical components that resist current and expends voltage within a circuit.
Batteries are electrical components that provide electrical energy.
Batteries have positive and negative terminals. The negative terminal is drawn with a short line, and the positive terminal is shown as a long line.
Switches turn the flow of current through a circuit pathway on and off. When the switch is open, no current flows because there is a gap in the circuit (Figure 3).
When the switch is closed, current can flow because the circuit is continuous (Figure 4).
A node (or junction) is a place where two or more circuit elements join together. Figure 5 below shows a single node (the black dot) formed by the junction of five electrical components (abstractly represented by orange rectangles).
DC circuit types
A simple circuit contains the minimum amount of components that allow it to be a functional electric circuit: a voltage source (battery), a resistor , and a loop of wires for current to flow around (see Figure 6 below). We usually ignore any resistance from the wires.
In a simple circuit, the voltage supplied by the battery is the voltage expended by the resistor , and there is only one current in the circuit.
A closed circuit has a continuous pathway for current to flow through. In other words, there are no gaps in the circuit.
An open circuit has a gap in the circuit that does not allow current to flow through. The gap can be caused by an open switch, a broken component, or broken wire.
A short is a pathway of zero resistance within a circuit (see the blue wire in Figure 9). When there is a short circuit, all the current flows across the short because the current prefers the path of least resistance.
Figure 10 below shows how closing a switch can divert all the current from resistor . When switch is open (see Figure 10A), the current flows out of the positive terminal of the battery towards node . Since the switch is open, no current flows through the switch and all the current flows through resistor . When the switch is closed (see Figure 10B), it forms a short around resistor . Now, once the current reaches , the current bypasses and flows through the switch.
For deeper explanations on electrical power, see our video on power used by a resistor.
To check your understanding and work toward mastering these concepts, check out our exercises:
Want to join the conversation?
- Why doesn't some of the current flow through resistor R2 in Figure 10B?(1 vote)
- Actually, there are charges flowing through R2; it's just that the path of least resistance will be preferred and so will have a considerably larger current compared to the path with the resistor.(10 votes)
- is power equal to thermal energy released by the resistor in joules per second(2 votes)
- In case the circuit only contains the resistor, the total power is indeed equal to the thermal energy released by the resistor. (J/s)(2 votes)
- In case the circuit only contains the resistor, the total power is indeed equal to the thermal energy released by the resistor. (J/s)(1 vote)