Wednesday, January 24, 2018

IAM Search

DC Electrical Sources and Loads

Sixth Part of of DC Electricity for Industrial Instrumentation

By definition, and source is a device that inputs energy into a system, while a load is a device that extracts energy from a system. Examples of typical electrical sources include generators, photovoltaic cells, thermopiles, and primary-cell batteries. Examples of typical electrical loads include resistors, lamps, and electric motors.

In a working circuit, electrical sources and loads may be easily distinguished by comparison of their current directions and voltage drop polarities. An electrical source always manifests a voltage polarity in a direction that assists the direction of charge flow. An electrical source always manifests a voltage polarity in a direction that opposes the direction of charge flow.

The convention used to designate direction of current (charge flow) becomes very important here. Since there are two commonly accepted notations – electron flow and “conventional” flow, exactly opposite of each other – it is easy to become confused.

First we see a diagram showing a source and a load, using electron flow notation. Electrons, being negatively charged particles, are repelled by the negative (-) poles of both source and load, and attracted to the positive (+) poles of both source and load. The difference between source and load is that the source device motivates the flow of electrons while the load device resists the flow of electrons:

 

Sources_Loads_Fig_024.JPG

Next we see a diagram showing the same source and load, this time using “conventional” flow notation to designate the direction of current. Here we must imagine positively-charged carriers moving through the wires instead of electrons. These positive charge carriers are repelled by any positive (+) pole and attracted to any negative (-) pole. Viewed in this light, we see the exact same principle at work: the source device is seen to motivate the flow of these positive charge carriers while the load device resists the flow:

 

Sources_Loads_Fig_025.JPG

In later parts, we encounter devices with the ability to act as sources and loads at different times. Both capacitors and inductors have the ability to temporarily contribute to and extract energy from electrical circuits, both having the ability to act as energy storage devices.

 

Click here to go to the contents page of Basic DC Electricity for Industrial Instrumentation

Click here to go back reading on the Kirchhoff's Laws - Fifth Part of DC electricity for Industrial Instrumentation

Click here to continue reading on the Resistors - Seventh Part of DC electricity for Industrial Instrumentation

Go Back to Lessons in Instrumentation Table of Contents

Comments (0)Add Comment

Write comment

security code
Write the displayed characters


busy

Promotions

  • ...more

Disclaimer

Important: All images are copyrighted to their respective owners. All content cited is derived from their respective sources.

Contact us for information and your inquiries. IAMechatronics is open to link exchanges.

IAMechatronics Login