Variable capacitors can store different amounts of electricity and are commonly used in radios to tune into different stations. They come in two types, air and vacuum, and can be controlled mechanically or electronically. The main advantage is the ability to adjust the capacitor without needing a different one for each frequency, but the drawback is their limited range and small capacity.
A variable capacitor is a special type of capacitor, most commonly used for tuning radios, that allows you to alter the amount of electric charge it can hold within a certain range, measured in a unit known as a farad. Ordinary capacitors build up and store an electric charge until they are ready for use. While a variable capacitor stores charge equally, it can be adjusted as often as desired to store different amounts of electricity. Because the variable capacitor’s most common use is in the tuning mechanisms of radios and older televisions, it is often called a tuning capacitor or variable tuning capacitor.
When changing a variable capacitor, the user is actually changing its capacitance. Capacity indicates the amount of energy that the capacitor can store. A larger capacity means more stored energy. This energy is measured in farads, but since a variable capacitor typically has a very small capacity, a smaller unit known as a picofarad is used instead.
Two types of variable capacitors include air variable capacitors and vacuum variable capacitors. While each performs the same function, a high vacuum is used instead of air to insulate the condenser. This allows for a larger capacitance to be produced in a smaller sized capacitor. Variable capacitors can also be controlled mechanically or electronically. Electronically controlled capacitors change their capacitance based on the applied DC voltage, while mechanically controlled versions are designed so that parts can be moved to increase or decrease the capacitance.
One of the most common uses of variable capacitors is in radios to allow the radio to tune into different stations. The capacitor is part of an LC circuit where L stands for inductor and C stands for capacitor. This inductor/capacitor combination uses the variable capacitor to alter the frequency that passes through the LC circuit and thereby connect with radio stations, each operating on a different frequency that the LC circuit must match in order to receive.
The ability to change the amount of electric charge it can hold is the main advantage of the variable capacitor over a regular capacitor. Allows the user to adjust the capacitor on items, such as radios, that constantly need to connect with different frequencies. Switching back and forth like this without variable capacitors would require a different capacitor for each frequency and would be impractical, if possible at all. The main drawback is the relatively small range they can cover. Typically they only change in a limited range and these values are of small capacity to begin with.
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