Introduction to Robotics/Electrical Components/Lecture/Teachers

Electricity Flowing in a Circuit

Electricity flows through circuits in the same way as water flows through pipes. Water only flows where the pipes are properly connected. Likewise, electricity will only flow where the components and wires are properly connected.

Notice also that electricity will only flow in a "complete circuit". Electricity must come from a source, and must go to a ground.

There are two quantities that we need to measure when dealing with electricity: Voltage and Current.

Voltage

Voltage is a measure of the "pressure" of the electricity. More voltage means more potential for the electricity to flow.

Current

Current is a measure of the "amount" of the electricity. More current means more electrons are flowing.

Resistors: Resisting current

Resistors are said to "resist current". At the same pressure (voltage), resistors cause less current to flow. Resistors are measured in units called "Ohms", and are labled with a Ω (greek capital omega).

For the same pressure, more ohms means less current, and fewer ohms means more current.

Ohm's Law

The relationship between current, voltage, and resistance is shown by Ohm's Law:

$V=IR$

Resistor Color Codes

Resistor values are shown using a special color code. A resistor will have 4 colored bands on it, one of the bands will be gold or silver. To read a resistor, put the gold/silver band on the right. The first two bands on the left are the digits, and the third band is an exponent.

To calculate the value of a resistor, we take the first two digits to form a 2-digit number, and we multiply it by 10 to the power of the third band. For instance, if our resistor was:

Then the value of the resistor would be:

$25\times 10^4=250000=250k\mathrm{\Omega }$

The fourth band is a "tolerance" band, or an error code. Silver means the resistor has a 10% error, and gold means the resistor has a 5% error.