- Current doesn't flow in an open circuit.
- Examples of open circuits include a broken wire, an open switch, and a burnt out light bulb.
- An open circuit has infinite resistance.
- In other words, an open circuit resists the flow of electricity to such a degree that no current flows.
- When a wire is connected across a component having
resistance, all the current will flow through the wire, and none will
flow through the component.
- The wire is said to be creating a short circuit (even if it's a long wire).
- When we say that a wire is connected across a component,
one end of the wire is connected to one end of the component, and the
other end of the wire is connected to the other end of the component.
In other words, the wire and the component are in parallel.
- When we draw schematics, it is assumed that we are using ideal wire and ideal meters.
- Ideal wire has no resistance.
- The resistance of an ideal wire is zero ohms.
- In other words, ideal wire does not resist the flow of electricity at all.
- An ideal voltmeter acts like an open circuit.
- In other words, no current flows through an ideal voltmeter.
- Real voltmeters (except for very cheap ones) have at least 10 M ohms of resistance. (10,000,000 ohms).
- Except for rare cases, we can assume that real voltmeters act like ideal voltmeters.
- An ideal ammeter acts like a piece of ideal wire.
- Except for rare cases, we can assume that real ammeters act like ideal ammeters.
- If you connect an ammeter across a component, you have
shorted out that component, and no current will flow through the
component.
- When no current is flowing through a component, there is no
voltage across that component (unless the component is an open circuit,
such as an open switch).
- Kirchhoff's voltage law: For any loop in a circuit, the sum of the voltage rises must equal the sum of the voltage drops.
- For electrical circuits (as opposed to electronics
circuits), there is only one voltage rise, namely the voltage source
coming from the power lines.
- Kirchhoff's current law: For any node, the sum of the
currents entering the node must equal the sum of the currents exiting
the node.
- In a 120 V. circuit, if you have a switch in series with a
load (such as a light), and the switch is open, the voltage across the
switch will be 120 V., and the voltage across the light will be zero.
- Ohm's law: I = V/R
- I is current (amperes)
- V is voltage (volts)
- R is resistance (ohms)
- Power = current x voltage
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