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July 28th, 2010
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July 28th, 2010
Volts, amps, and ohms
This is part two in our series on basic electronics. Part one is Electron, Proton, Neutron.
An electrical circuit allows electrons to flow from one side of the circuit to the other. The two ends of the circuit have a difference in electrical charge. One side is more positively charged then the other. Electrons are attracted to the positive side and move through the circuit. The electrons move from the negative side of the circuit to the positive but we say the electrical current flows from the positive to the negative. It is the attractive force emanating from the positive side of the circuit that we call the current.
This diagram shows a simple LED driver circuit. When the battery is connected the positive end of the battery pulls electrons from the negative end of the battery and through the circuit. This circuit has three basic properties we can use for measurement and analysis. They are voltage, current, and resistance.
Voltage
The amount of difference in electrical charge between the two sides of the circuit is called the voltage. Higher voltage power sources will have more attractive force. Voltage can be considered electrical pressure pulling electrons through a circuit.
Current
While the voltage moves the electrons through the circuit they cannot all go at once. The rate at which the electrons move through the circuit is called the current. We measure the current in amperes. One amp is about 6.241×1018 electrons passing through a point in a circuit in one second.
note: 6.241x1018 is an easier way to write a big number. It stands for the number 6,241,000,000,000,000,000.
Resistance
Because of the electrical pressure the electrons would like to move at a very high current but some materials conduct electricity better then others. Materials that have a high resistance conduct electricity less well. Resistance limits the flow of electrons between the two ends of the circuit. We measure resistance in units called ohms (Ω). One ohm is defined as the amount of resistance you have in a conductor when applying one volt of electrical pressure creates one amp of current.
Ohm’s law
Voltage, current, and resistance have a mathematical relationship which we can use to calculate the properties of the circuit. Ohm’s law states that the current is directly proportional to the voltage and inversely proportional to the resistance. The formula looks like:
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The current equals the voltage divided by the resistance. |
It can also be written:
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The voltage equals the current multiplied by the resistance. |
Or, you can write it like this:
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The resistance equals the voltage divided by the current. |
They are all the same. Using these equations, if you know any two of the values you can calculate the third.
Looking again at our LED driver circuit let’s try to figure out the current through the circuit. If we use a 3 volt battery to power the circuit and a 220 Ohm resistor then what should the current through the circuit be?
So lets’ recap. Voltage is like electrical pressure. It is the amount of difference in charge between the two sides of the circuit. Current is how quickly the charge moves from one side to another. Resistance holds back the electrical pressure, impeding the current. Higher voltage creates high current. High resistance causes lower current.
Stay tuned for our next article.
July 7th, 2010
Electricity – Electron, Proton, Neutron
This is part one of our basic electronics series.
This article presents an extremely simplified explanation of electrical phenomena as an introduction to its practical application.
All matter is made of atoms. Atoms are made up of tiny particles we call electrons, protons and neutrons. Protons and, usually, neutrons form the center (nucleus) of the atom. Electrons spin around the nucleus.
All matter is made up of these few parts. It is only the number and arrangement of the particles that makes one type of matter different from another.
These particles can have an electrical charge. Protons have a positive electrical charge and electrons have a negative electrical charge. Positive and negative are attracted to one another while like charges repel one another.
The electrons spin in different levels called electron shells. Electrons in the smaller/closer electron shells have less energy then electrons in the further/larger shells. Electrons and protons usually balance out so the overall electrical charge of an atom is neutral. Not positive or negative.
If the protons and electrons are out of balance the atom has an electrical charge. An atom with more electrons then protons has a negative electrical charge. Electrons can move from one atom to another because it is attracted to positively charged atoms and repulsed by negatively charged atoms.
Conductors are materials that conduct electricity well. Conductors, like a copper wire, are made up of atoms that gain and lose electrons easily. Allowing the electrons to be passed down the wire. Insulators are materials that do not allow electrons to move easily, like the rubber coating on your copper wire.
The electrons actually move down the wire quite slowly. As they move they repulse the electrons in front of them creating a wave of repulsive force which moves down the wire very quickly.
These electrons can have a number of different effects as they move. The can bump into atoms on the way and cause them to move around which is heat. They can move up and down the electron shells of atoms. If they move down to lower energy shells they give up the excess energy in the form of photons (light). They also create invisible electromagnetic waves as they travel. These waves can create electric current in matter that they touch as well as create motion by the attraction and repulsion of magnetic waves.
We use all of these properties of electrons in different ways. We create heat to cook food and keep us warm. We create light to see by. We create motion to turn fans and push trains. We also use it to send and receive information. We can use electricity to send information through the wires or create electromagnetic waves to send information through the air.
Stay tuned for the next article in our series where we will talk about electric voltage, current, and resistance.
September 30th, 2009
LEDs: Why do different LEDs require different voltages?
If you are like me, you probably have a bag of assorted LEDS in a dark corner of your toolbox or in your Discover Electronics kit. You want to use one of those LEDs for your next big electronics project but you’re not sure what voltage is required. Why can’t all LEDS require the same voltage?
A light emitting diode (LED) functions in the same way as a normal diode. There are two nodes within an LED. One node is made of a processed material called P-type semiconductor. The other node is made of a N-type semiconductor. When electrons flow from the P-type semiconductor to the N-type semiconductor they fall to a lower energy level and release electrons in the form of light. The amount of energy required to release an electron in this way is called the band gap. Different color LEDs are created by using semiconductors with lower and higher band gaps. A red LED is made from a low band gap material called Aluminum gallium arsenide and therefore requires a lower amount of voltage to produce light.
June 30th, 2009
New Tutorials Coming Soon!
Sparkle Labs is creating a set of tutorials on the basics of electronics.
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