What is Polarity?

Polarity is a term used in electricity, magnetism and electronic signaling, just to name a few areas. Polarity is defined as, the condition of a body or system in which it has opposing physical properties at different points, especially, magnetic poles or electric charge.

 

In the case of electric current running between two points, or poles, one of the poles will have more electrons than the other. The pole with more electrons is said to have negative polarity. The pole with fewer electrons then has a positive polarity. When the two poles are connected by a wire, electrons flow from the negative pole toward the positive pole. This flow is called an electric current.

 

In a direct current (DC) circuit, one pole is always negative and the other pole is always positive with the electrons only flowing in one direction. In an alternating current (AC) circuit the two poles alternate between negative and positive with the direction of the electrons flowing in reverse.

 

Testing Polarity

Alternating current (AC) can be tested with a multimeter or volt ohm meter. Testing with a multimeter usually involves touching positive and negative leads from the meter to the wiring being tested. A flashing negative sign (“-”) before the numerical reading on the meter indicates that the polarity is incorrect.

 

Reversed Polarity

If you discover that one of your home’s wall outlets has reversed polarity, correcting the problem isn’t difficult, however, you need to be careful you aren’t shocked or electrocuted. You should turn off your domestic electricity supply before inspecting the wiring. Positive wires, which are typically red or black, should be connected to the brass terminal. Neutral wires, which are typically white or gray, should be connected to the lighter-colored, chrome terminal.

 

If the wires aren’t connected properly, then you will have reversed polarity and the result is the current going in the opposite direction of which it is intended. This can result in electrical shock to anyone touching the device or the outlet, and even damage to the device itself.

 

Diodes

Diodes are unique in the idea that they only allow current to flow in one direction, and they are always polarized. There are two terminals on a diode, the anode is the positive terminal and the cathode is the negative terminal.

 

Current is only able to flow from the anode to the cathode in regards to a diode. It is for this reason that a diode needs to be connected in the proper direction. This is why every diode should have the anode and the cathode pins clearly marked. In most cases, the diode will have a line near the cathode pin. This line will usually match the vertical line in the diode circuit symbol.

 

LEDs

An LED is a light-emitting diode. As with all diodes, LEDs are also polarized. There are a few different ways to determine which pin is the positive and which is the negative. The longer leg on the LED is the anode, or the positive pin.

 

Another way to determine the positive anode pin, especially if the legs have been trimmed to the same size, is by looking for the flat edge on the LED. The pin closest to the flat edge is the negative cathode pin.

 

Integrated Circuit Polarity

Integrated circuits (ICs) can have several pins and each pin has a unique function and position. If the polarity on an IC isn’t kept straight, there is a good chance that the whole circuit can be shorted out. This is why it is important to be able to find the proper flow of the polarity.

 

Through-hole ICs usually come in a dual-inline package (DIP). This consists of two rows of pins, each of them spaced 0.1” wide to straddle the center of the breadboard. There is usually a notch to indicate which of the pins is the first on the DIP ICs. If a notch isn’t present, the IC may have an etched dot in the casing near the number one pin.

 

Polarity of a Battery

Finding the polarity on most batteries is simple, because the positive and negative terminals will be marked with a “+” or “-” symbol. Another standard practice is the use of a red wire for positive and a black wire for a negative connection.


Finding and using the proper polarity and the correct flow of current is crucial to the safe and effective use of electricity. With some research and, in many cases, common sense you can make sure your device is running properly.

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