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Circuits, Ohm’s Law

& Kirchhoff’s

Rules

Schematic Diagrams

A Schematic diagram uses symbols to represent the different components of the circuit. In order for a circuit diagram to be useful it must be organized correctly as well as:•Neat and tidy (i.e. use a ruler)•Make all connecting wires and leads with straight-lines at 90o angles (i.e. perpendicular).•Avoid drawing conductors over top one another (use a semi-circle if unavoidable)•Your finished diagram should be square or rectangular.

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Schematic Diagrams

Examples:

Schematic Diagrams

Examples:

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Schematic Diagrams

Examples:

Schematic Diagrams

Examples:

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Ohm’s Law

In 1827, Georg Ohm a German physicist found a relationship between voltage, current and resistance. Now referred to Ohm’s Law states that “the electrical resistance of a circuit is directly proportional to voltage and inversely proportional to current”. The unit for resistance is the Ohm (W).

Ohm’s Law

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Circuits

To perform this lab, we will need the following materials:

• DMM w/ Cables• Assortment of Resistors• Power Supply / Batteries• Breadboard• Wire

Series Circuits

In a series circuits there is only one (1) path for current to flow. Since there is only one path for electrons to travel, the current in each part of a series circuit is equal. In addition, each load in the circuit uses a portion of the voltage. The sum of the voltages lost by each load is equal to the total voltage supplied by the battery (Conservation of Energy).

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Series Circuits

When resistors are placed in series, the total resistance of the circuit increases and therefore the total current through the circuit decreases.

Series Circuits

Example:

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Kirchhoff’s Voltage Rule

“The sum of all the voltage drops around any closed loop is equal to zero”

+5V -2.5V-2.5V

Loop

Parallel Circuits

In a parallel circuit there is a minimum of two (2) paths that the current can take, as a result the current is divided between each of the paths. The point where the current splits is called a junction point.

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Parallel Circuits

When resistors are placed in parallel the total resistance of the circuit decreases and therefore the total current increases. The voltage in a parallel circuit is the same for each path.

Parallel Circuits

Example:

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Kirchhoff’s Current Rule

When the current splits no current is created or destroyed (Conservation of Charge), it only splits between each path. The pathway with less resistance will allow more electrons to travel on it and therefore will have a greater current than a pathway with more resistance.

Kirchhoff’s Current Rule

“The current entering a junction is equal to the current leaving the junction”

5A3A

2 A